Tropical cyclone

Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004.

In meteorology, a tropical cyclone (also referred to as a tropical depression, tropical storm, typhoon, or hurricane depending on strength and geographical context) is a type of low pressure system which generally forms in the tropics. While they can be highly destructive, tropical cyclones are an important part of the atmospheric circulation system, which moves heat from the equatorial region toward the higher latitudes.

Terms for tropical cyclones

Eye of Typhoon Odessa, Pacific Ocean, August 1985

Terms used in weather reports for tropical cyclones that have surface winds over 64 knots (73.6 mph) or 32 m/s vary by region:

  • Hurricane: Atlantic basin and North Pacific Ocean east of the dateline
  • Typhoon: Northwest Pacific west of the dateline
  • Severe tropical cyclone: Southwest Pacific west of 160°E and the southeast Indian Ocean east of 90°E
  • Severe cyclonic storm: North Indian Ocean
  • Tropical cyclone: Southwest Indian Ocean and the South Pacific east of 160°E.
  • Cyclone (unofficially): South Atlantic Ocean

There are many regional names for tropical cyclones, including Bagyo in the Philippines and Taino in Haiti.

Etymology

The word typhoon has two possible origins:

  • From the Chinese 大風 (daaih fūng (Cantonese); dà fēng (Mandarin)) which means "great wind". (The Chinese term as 颱風 táifēng, and 台風 taifu in Japanese, has an independent origin traceable variously to 風颱, 風篩 or 風癡 hongthai, going back to Song 宋 (960-1278) and Yuan 元(1260-1341) dynasties. The first record of the character 颱 appeared in 1685's edition of Summary of Taiwan 臺灣記略).
  • From Urdu, Persian or Arabic ţūfān (طوفان) < Greek tuphōn (Τυφών).

Portuguese tufão is also related to typhoon. See tuphōn for more information.

The word hurricane is derived from the name of a native Caribbean Amerindian storm god, Huracan, via Spanish huracán.

The word cyclone is from the Greek "κύκλος", meaning "circle." An Egyptian word Cykline meaning to "to spin" has been cited as a possible origin. [citation needed]

Mechanics of tropical cyclones

Hurricanes form when the energy released by the condensation of moisture in rising air causes a positive feedback loop. The air heats up, rising further, which leads to more condensation. The air flowing out of the top of this “chimney” drops towards the ground, forming powerful winds.

Structurally, a tropical cyclone is a large, rotating system of clouds, wind and thunderstorms. Its primary energy source is the release of the heat of condensation from water vapor condensing at high altitudes, the heat ultimately derived from the sun. Therefore, a tropical cyclone can be thought of as a giant vertical heat engine supported by mechanics driven by physical forces such as the rotation and gravity of the Earth. Continued condensation leads to higher winds, continued evaporation, and continued condensation, feeding back into itself. This gives rise to factors that give the system enough energy to be self-sufficient and cause a positive feedback loop where it can draw more energy as long as the source of heat, warm water, remains. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The orbital revolution of the Earth causes the system to spin, an effect known as the Coriolis force, giving it a cyclone characteristic and affecting the trajectory of the storm.

The factors to form a tropical cyclone include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist and allow it to create a feedback loop by maximizing the energy intake possible, for example, such as high winds to increase the rate of evaporation, they can combine to produce the violent winds, incredible waves, torrential rains, and floods associated with this phenomenon.

Condensation as a driving force is what primarily distinguishes tropical cyclones from other meteorological phenomena, and because this is strongest in a tropical climate, this defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclones, for example, draw their energy mostly from pre-existing horizontal temperature gradients in the atmosphere. In order to continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the atmospheric moisture needed. The evaporation of this moisture is accelerated by the high winds and reduced atmospheric pressure in the storm, resulting in a positive feedback loop. As a result, when a tropical cyclone passes over land, its strength diminishes rapidly.

Scientists at the National Center for Atmospheric Research estimate that a hurricane releases heat energy at the rate of 50 to 200 trillion watts -- about the amount of energy released by exploding a 10-megaton nuclear bomb every 20 minutes [1].

While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine. This outflow produces high, thin cirrus clouds that spiral away from the center. The high cirrus clouds may be the first signs of an approaching hurricane.

Formation

Waves in the trade winds in the Atlantic Ocean—areas of converging winds that move along the same track as the prevailing wind—create instabilities in the atmosphere that may lead to the formation of hurricanes.

The formation of tropical cyclones is the topic of extensive ongoing research, and is still not fully understood. Five factors are necessary to make tropical cyclone formation possible:

  1. Sea surface temperatures above 26.5 degrees Celsius (79.7 degrees Fahrenheit) to at least a depth of 50 meters (164 feet). The moisture in the air above the warm water is the energy source for tropical cyclones.
  2. Upper-atmosphere conditions conducive to thunderstorm formation. Temperature in the atmosphere must decrease quickly with height, and the mid-troposphere must be relatively moist.
  3. A pre-existing weather disturbance. This is most frequently provided by tropical waves—non-rotating areas of thunderstorms that move through tropical oceans.
  4. A distance of approximately 10 degrees or more from the equator, so that the Coriolis effect is strong enough to initiate the cyclone's rotation. (2004's Hurricane Ivan was the strongest storm to form closer than 10 degrees from the equator; it started forming at 9.7 degrees north.)
  5. Low vertical wind shear (change in wind speed or direction over height). High wind shear can break apart the vertical structure of a tropical cyclone.

Tropical cyclones occasionally form despite not meeting these conditions.

Only specific weather disturbances can result in tropical cyclones. These include:

  1. Tropical waves, or easterly waves, which, as mentioned above, are westward moving areas of convergent winds. This often assists in the development of thunderstorms, which can develop into tropical cyclones. Most tropical cyclones form from these. A similar phenomenon to tropical waves are West African disturbance lines, which are squally lines of convection that form over Africa and move into the Atlantic.
  2. Tropical upper tropospheric troughs, which are cold-core upper level lows. A warm-core tropical cyclone may result when one of these (on occasion) works down to the lower levels and produces deep convection.
  3. Decaying frontal boundaries may occasionally stall over warm waters and produce lines of active convection. If a low level circulation forms under this convection, it may develop into a tropical cyclone.

Times of formation

Worldwide, tropical cyclone activity peaks in late summer when water temperatures are warmest. However, each particular basin has its own seasonal patterns.

In the North Atlantic, a distinct hurricane season occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the North Atlantic hurricane season is September 10. The Northeast Pacific has a broader period of activity, but in a similar timeframe to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November.

In the Southern Hemisphere, tropical cyclone activity begins in late October and ends in May. Southern Hemisphere activity peaks in mid-February to early March.

Worldwide, an average of 80 tropical cyclones form each year.

Locations of formation

Most tropical cyclones form in a worldwide band of thunderstorm activity called the Intertropical convergence zone (ITCZ).

Nearly all of them form between 10 and 30 degrees of the equator and 87% form within 20 degrees of it. Because the Coriolis effect initiates and maintains tropical cyclone rotation, such cyclones almost never form or move within about 10 degrees of the equator [2], where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary if there is another source of initial rotation. These conditions are extremely rare, and such storms are believed to form at most once per century. Hurricane Ivan of 2004 developed within 10 degrees of the equator. A combination of a pre-existing disturbance, upper level divergence and a monsoon-related cold spell led to Typhoon Vamei at only 1.5 degrees north of the equator in 2001. It is estimated that such conditions occur only once every 400 years.

Major basins

There are seven main basins of tropical cyclone formation:

  • North Atlantic Basin: The most-studied of all tropical basins, it includes the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. Tropical cyclone formation here varies widely from year to year, ranging from over twenty to one per year. The average is about ten. The United States Atlantic coast, Mexico, Central America, the Caribbean Islands and Bermuda are frequently affected by storms in this basin. Venezuela, the south-east of Canada and Atlantic "Macaronesian" islands are also occasionally affected. The U.S. National Hurricane Center (NHC) based in Miami, Florida, issues forecasts for storms for all nations in the region; the Canadian Hurricane Centre, based in Halifax, Nova Scotia, also issues forecasts and warnings for storms expected to affect Canadian territory and waters. Hurricanes that strike Mexico, Central America, and Caribbean island nations, often do intense damage, as hurricanes are deadlier over warmer water. Additionally, they can hit the coast of the U.S., especially Florida, North Carolina, the U.S. Gulf Coast and occasionally New Jersey, New York and New England (usually hurricanes weaken to tropical storms before they reach these northern regions). The coast of Atlantic Canada receives hurricane landfalls on rare occasion, such as Hurricane Juan in 2003. Many of the more intense Atlantic storms are Cape Verde-type hurricanes, which form off the west coast of Africa near the Cape Verde islands.
  • Western North Pacific Ocean: Tropical storm activity in this region frequently affects China, Japan, the Philippines, and Taiwan, but also many other countries in South-East Asia, such as Vietnam, South Korea and Indonesia, plus numerous Oceanian islands. This is by far the most active basin, accounting for one-third of all tropical cyclone activity in the world. The eastern coasts of Taiwan and Philippines also have the highest tropical cyclone landfall frequency in the world. National meteorology organizations and the Joint Typhoon Warning Center (JTWC) are responsible for issuing forecasts and warnings in this basin.
  • Eastern North Pacific Ocean: This is the second most active basin in the world, and the most dense (a large number of storms for a small area of ocean). Storms that form here can affect western Mexico, Hawaii, northern Central America, and on extremely rare occasions, California. In the U.S., the Central Pacific Hurricane Center is responsible for forecasting the western part of this area while the National Hurricane Center is responsible for the eastern part.
  • South Western Pacific Ocean: Tropical activity in this region largely affects Australia and Oceania, and is forecast by Australia and Papua New Guinea.
  • Northern Indian Ocean: This basin is divided into two areas, the Bay of Bengal and the Arabian Sea, with the Bay of Bengal dominating (5 to 6 times more activity). This basin's season has an interesting double peak; one in April and May before the onset of the monsoon, and another in October and November just after. Hurricanes which form in this basin have historically cost the most lives — most notably, the 1970 Bhola cyclone killed 200,000. Nations affected by this basin include India, Bangladesh, Sri Lanka, Thailand, Myanmar, and Pakistan, and all of these countries issue regional forecasts and warnings. Rarely, a tropical cyclone formed in this basin will affect the Arabian Peninsula.
  • Southeastern Indian Ocean: Tropical activity in this region affects Australia and Indonesia, and is forecast by those nations.
  • Southwestern Indian Ocean: This basin is the least understood, due to a lack of historical data. Cyclones forming here impact Madagascar, Mozambique, Mauritius, and Kenya, and these nations issue forecasts and warnings for the basin.

Unusual formation areas

Hurricane Vince on October 9, 2005 at 2300 UTC near the Madeira Islands.

The following areas spawn tropical cyclones only very rarely.

  • South Atlantic Ocean: A combination of cooler waters, the lack of an ITCZ, and wind shear makes it very difficult for the South Atlantic to support tropical activity. However, three tropical cyclones have been observed here — a weak tropical storm in 1991 off the coast of Africa, Cyclone Catarina (sometimes also referred to as Aldonça), which made landfall in Brazil in 2004 at Category 1 strength, and a smaller storm in January 2004, east of Salvador, Brazil. The January storm is thought to have reached tropical storm intensity based on scatterometre winds.
  • Central North Pacific: Shear in this area of the Pacific Ocean severely limits tropical development. However, this region is commonly frequented by tropical cyclones that form in the much more favorable Eastern North Pacific Basin.
  • Eastern South Pacific: Tropical cyclone formation is rare in this region; when they do form, it is frequently linked to El Niño episodes. Most of the storms that enter this region formed farther west in the Southwest Pacific. They affect the islands of Polynesia in exceptional instances.
  • Mediterranean Sea: Storms which appear similar to tropical cyclones in structure sometimes occur in the Mediterranean basin. Such cyclones formed in September 1947, September 1969, January 1982, September 1983, and January 1995. However, there is debate on whether these storms were tropical in nature.
  • Northeastern Atlantic Ocean: In October 2005, Hurricane Vince formed near Madeira, then moved northeastward, passing south of the Portuguese south coast, and made landfall in southwestern Spain as a tropical depression. Vince's origin was the northeasternmost in the eastern Atlantic ever recorded, and Vince was the first storm in recorded history to reach the Iberian Peninsula as a tropical cyclone, i.e. before being transformed into an extratropical low or absorbed into other systems of low pressure.
  • Australia: SW Pacific Basin includes the eastern part of Australia and the Fiji area.
  • Australia: SE Indian Basin includes the eastern part of the Indian ocean and the northern and western part of the Australian basin.
  • Southern South China Sea Tropical cyclones normally do not develop in the Southern South China Sea due to its close proximity to the equator. Areas within ten degrees laditude of the equator do not experience a significant coriolis force, a vital ingredient in tropical cyclone formation. However, in December 2001, Typhoon Vamei formed in the Southern South China Sea and made landfall in Malaysia. It caused flooding in southern Malaysia and some damage in Singapore. It formed from a thunderstorm formation in Borneo that moved into the South China Sea.
  • The Great Lakes A storm system that appeared similar to a tropical cyclone formed in 1996 on Lake Huron it formed an eye and could have breifly been sub-tropical.

Average Season

Structure and classification

Structure of a hurricane

A strong tropical cyclone consists of the following components.

  • Surface low: All tropical cyclones rotate around an area of low atmospheric pressure near the Earth's surface. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level.
  • Warm core: Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation as moist air is carried upwards and its water vapor condenses. This heat is distributed vertically, around the center of the storm. Thus, at any given altitude (except close to the surface where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.
  • Central Dense Overcast (CDO): The Central Dense Overcast is a dense shield of very intense thunderstorm activity that make up the inner portion of the hurricane. This contains the eye wall, and the eye itself. The classic hurricane contains a symmetrical CDO, which means that it is perfectly circular and round on all sides.
  • Eye: A strong tropical cyclone will harbor an area of sinking air at the center of circulation. Weather in the eye is normally calm and free of clouds (however, the sea may be extremely violent). Eyes are home to the coldest temperatures of the storm at the surface, and the warmest temperatures at the upper levels. The eye is normally circular in shape, and may range in size from 8 km to 200 km (5 miles to 125 miles) in diameter. In weaker cyclones, the CDO covers the circulation center, resulting in no visible eye.
  • Eyewall: A band around the eye of greatest wind speed, where clouds reach highest and precipitation is heaviest. The heaviest wind damage occurs where a hurricane's eyewall passes over land.
  • Outflow: The upper levels of a tropical cyclone feature winds headed away from the center of the storm with an anticyclonic rotation. Winds at the surface are strongly cyclonic, weaken with height, and eventually reverse themselves. Tropical cyclones owe this unique characteristic to the warm core at the center of the storm.

Intensities of tropical cyclones

Tropical cyclones are classified into three main groups: tropical depressions, tropical storms, and a third group whose name depends on the region.

A tropical depression is an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of less than 17 metres per second (33 knots, 38 mph, or 62 km/h). It has no eye, and does not typically have the spiral shape of more powerful storms. It is already becoming a low-pressure system, however, hence the name "depression".

A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 and 33 meters per second (34–63 knots, 39–73 mph, or 62–117 km/h). At this point, the distinctive cyclonic shape starts to develop, though an eye is usually not present. Government weather services assign first names to systems that reach this intensity (thus the term named storm).

At hurricane and typhoon intensity, a tropical cyclone tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of the circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the eyewall, an area about 10 to 50 miles (16 to 80 kilometers) wide in which the strongest thunderstorms and winds circulate around the storm's center.

The circulation of clouds around a cyclone's center imparts a distinct spiral shape to the system. Bands or arms may extend over great distances as clouds are drawn toward the cyclone. The direction of the cyclonic circulation depends on the hemisphere; it is counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere. Maximum sustained winds in the strongest tropical cyclones have been measured at more than 85 m/s (165 knots, 190 mph, 305 km/h). Intense, mature hurricanes can sometimes exhibit an inward curving of the eyewall top that resembles a football stadium: this phenomenon is thus sometimes referred to as stadium effect.

Eyewall replacement cycles naturally occur in intense tropical cyclones. When cyclones reach peak intensity they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 5 to 15 miles. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening (i.e. the maximum winds die off a bit and the central pressure goes up). Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger.

Categories and ranking

Hurricanes are ranked according to their maximum winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest maximum winds, a Category 5 hurricane has the highest. The rankings are not absolute in terms of effects. Lower-category storms can inflict greater damage than higher-category storms, depending on factors such as local terrain and total rainfall. For instance, a Category 2 hurricane that strikes a major urban area will likely do more damage than a large Category 5 hurricane that strikes a mostly rural region. In fact, tropical systems of less than hurricane strength can produce significant damage and human casualties, especially from flooding and landslides.

The National Hurricane Center classifies hurricanes of Category 3 and above as Major Hurricanes. The Joint Typhoon Warning Center classifies typhoons with wind speeds of at least 150 mi/h (67 m/s or 241 km/h, equivalent to a strong Category 4 storm) as Super Typhoons.

The definition of sustained winds recommended by the World Meteorological Organization (WMO) and used by most weather agencies is that of a 10-minute average. The U.S. weather service defines sustained winds based on 1-minute average speed measured about 10 meters (33 ft) above the surface.

Other storm systems

Many other forms of cyclone can form in nature. Several of these relate to the formation or dissipation of tropical cyclones.

Extratropical cyclone

An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses; more rarely, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "comma-shaped" cloud pattern. Extratropical cyclones can also be dangerous because their low-pressure centers cause powerful winds.

Subtropical storm

A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitude, from the equator to 50°. Although subtropical storms rarely attain hurricane-force winds, they may become tropical in nature as their core warms.

European windstorms

In the United Kingdom and Europe, some severe northeast Atlantic cyclonic depressions are referred to as "hurricanes," even though they rarely originate in the tropics. These European windstorms can generate hurricane-force winds but are not given individual names. However, two powerful extratropical cyclones that ravaged France, Germany, and the United Kingdom in December 1999, "Lothar" and "Martin", were named due to their unexpected power (equivalent to a category 1 or 2 hurricane). In British Shipping Forecasts, winds of force 12 on the Beaufort scale are described as "hurricane force."

Movement and track

Large-scale winds

Although tropical cyclones are large systems generating enormous energy, their movements over the earth's surface are often compared to that of leaves carried along by a stream. That is, large-scale winds—the streams in the earth's atmosphere—are responsible for moving and steering tropical cyclones. The path of motion is referred to as a tropical cyclone's track.

The major force affecting the track of tropical systems in all areas are winds circulating around high-pressure areas. Over the North Atlantic Ocean, tropical systems are steered generally westward by the east-to-west winds on the south side of the Bermuda High, a persistent high-pressure area over the North Atlantic. Also, in the area of the North Atlantic where hurricanes form, trade winds, which are prevailing westward-moving wind currents, steer tropical waves (precursors to tropical depressions and cyclones) westward from off the African coast toward the Caribbean and North America.

Coriolis effect

The earth's rotation also imparts an acceleration (termed the Coriolis Acceleration or Coriolis Effect). This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents (i.e. in the north, the northern part of the cyclone has winds to the west, and the Coriolis force pulls them slightly north. The southern part is pulled south, but since it is closer to the equator, the Coriolis force is a bit weaker there). Thus, tropical cyclones in the Northern Hemisphere, which commonly move west in the beginning, normally turn north (and are then usually blown east), and cyclones in the Southern Hemisphere are deflected south, if no strong pressure systems are counteracting the Coriolis Acceleration. The Coriolis acceleration also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds. (Much of that is due to the conservation of angular momentum - air is drawn in from an area much larger than the cyclone such that the tiny angular velocity of that air will be magnified greatly when the distance to the storm center shrinks.)

Interaction with high and low pressure systems

Finally, when a tropical cyclone moves into higher latitude, its general track around a high-pressure area can be deflected significantly by winds moving toward a low-pressure area. Such a track direction change is termed recurve. A hurricane moving from the Atlantic toward the Gulf of Mexico, for example, will recurve to the north and then northeast if it encounters winds blowing northwestward toward a high-pressure system passing over North Africa. Many tropical cyclones along the coast. East Coast and in the Gulf of Mexico are eventually forced toward the northeast by high-pressure areas which move from west to east over North Africa.

Forecasting

Hurricane Epsilon strengthened and organized in the Central North Atlantic Ocean despite highly unfavorable conditions. This unusual system defied most NHC forecasts and demonstrated the difficulties of predicting tropical cyclones.

Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system.

With their understanding of the forces that act on tropical cyclones, and a wealth of data from earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. High-speed computers and sophisticated simulation software allow forecasters to produce computer models that forecast tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. But while track forecasts have become more accurate than 20 years ago, scientists say they are less skillful at predicting the intensity of tropical cyclones. They attribute the lack of improvement in intensity forecasting to the complexity of tropical systems and an incomplete understanding of factors that affect their development.

Landfall

Officially, "landfall" is when a storm's center (the center of the eye, not its edge) reaches land. Naturally, storm conditions may be experienced on the coast and inland well before landfall. In fact, for a storm moving inland, the landfall area experiences half the storm before the actual landfall. For emergency preparedness, actions should be timed from when a certain wind speed will reach land, not from when landfall will occur.

For a list of notable and unusual landfalling hurricanes, see list of notable tropical cyclones.

Dissipation

A tropical cyclone can cease to have tropical characteristics in several ways:

  • It moves over land, thus depriving it of the warm water it needs to power itself, and quickly loses strength. Most strong storms lose their strength very rapidly after landfall, and become disorganized areas of low pressure within a day or two. There is, however, a chance they could regenerate if they manage to get back over open warm water. If a storm is over mountains for even a short time, it can rapidly lose its structure. However, many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall which can lead to deadly floods and mudslides.
  • It remains in the same area of ocean for too long, drawing heat off of the ocean surface until it becomes too cool to support the storm. Without warm surface water, the storm cannot survive.
  • It experiences wind shear, causing the convection to lose direction and the heat engine to break down.
  • It can be weak enough to be consumed by another area of low pressure, disrupting it and joining to become a large area of non-cyclonic thunderstorms. (Such, however, can strengthen the non-tropical system as a whole.)
  • It enters colder waters. This does not necessarily mean the death of the storm, but the storm will lose its tropical characteristics. These storms are extratropical cyclones.
  • An outer eye wall forms (typically around 50 miles from the center of the storm), choking off the convection toward the inner eye wall. Such weakening is generally temporary unless it meets other conditions above.

Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane force) winds and drop several inches of rainfall. When a tropical cyclone reaches higher latitudes or passes over land, it may merge with weather fronts or develop into a frontal cyclone, also called extratropical cyclone. In the Atlantic ocean, such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane-force wind speeds when they reach Europe as a European windstorm.

Artificial dissipation

In the 1960s and 1970s, the United States government attempted to weaken hurricanes in its Project Stormfury by seeding selected storms with silver iodide. It was thought that the seeding would cause supercooled water in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds. The winds of Hurricane Debbie dropped as much as 30 percent, but then regained their strength after each of two seeding forays. In an earlier episode, disaster struck when a hurricane east of Jacksonville, Florida, was seeded, promptly changed its course, and smashed into Savannah, Georgia[citation needed]. Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10 percent chance of making landfall within 48 hours. The project was dropped after it was discovered that eyewall replacement cycles occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. Today it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.[3]

Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing icebergs into the tropical oceans; dropping large quantities of ice into the eye at very early stages so that latent heat is absorbed by ice at the entrance (storm cell perimeter bottom) instead of heat energy being converted to kinetic energy at high altitudes vertically above; covering the ocean in a substance that inhibits evaporation; or blasting the cyclone apart with nuclear weapons. These approaches all suffer from the same flaw: tropical cyclones are simply too large for any of them to be practical [4].

However, it has been suggested by some that we can change the course of a storm during its early stages of formation, (detailed by an article, Controlling Hurricanes, Scientific American, 2005), such as using satellite to alter the environmental conditions or, more realistically, spreading degradable film of oil over the ocean, which prevent water vapor from fueling the storm.

Monitoring, observation and tracking

Intense tropical cyclones pose a particular observation challenge. As they are a dangerous oceanic phenomenon, weather stations are rarely available on the site of the storm itself. Surface level observations are generally available only if the storm is passing over an island or a coastal area, or it has overtaken an unfortunate ship. Even in these cases, real-time measurement taking is generally possible only in the periphery of the cyclone, where conditions are less catastrophic.

It is however possible to take in-situ measurements, in real-time, by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by US government hurricane hunters [5]. The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engine turboprop cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch GPS dropsondes inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface.

A new era in hurricane observation began when a remotely piloted Aerosonde, a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare[6].

Tropical cyclones far from land are tracked by weather satellites capturing visible and infrared images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based Doppler radar. Radar plays a crucial role around landfall because it shows a storm's location and intensity minute by minute.

Recently, academic researchers have begun to deploy mobile weather stations fortified to withstand hurricane-force winds. The two largest programs are the Florida Coastal Monitoring Program [7] and the Wind Engineering Mobile Instrumented Tower Experiment [8]. During landfall, the NOAA Hurricane Research Division compares and verifies data from reconnaissance aircraft (which includes wind speed data taken at flight level and from GPS dropwindsondes and stepped-frequency microwave radiometers) to wind speed data transmitted in real time from weather stations erected near or at the coast. The National Hurricane Center uses the data to evaluate conditions at landfall and to verify forecasts.

Naming of tropical cyclones

Storms reaching tropical storm strength (winds exceeding 17 metres per second, 38 mph, or 62 km/h) are given names, to assist in recording insurance claims, to assist in warning people of the coming storm, and to further indicate that these are important storms that should not be ignored. These names are taken from lists which vary from region to region and are drafted a few years ahead of time. The lists are decided upon, depending on the regions, either by committees of the World Meteorological Organization (called primarily to discuss many other issues), or by national weather services involved in the forecasting of the storms.

Each year, the names of particularly destructive storms (if there were any) are "retired" and new names are chosen to take their place.

Naming schemes

The WMO's Regional Association IV Hurricane Committee selects the names for Atlantic Basin and central and eastern Pacific storms.

In the Atlantic and Eastern North Pacific regions, feminine and masculine names are assigned alternately in alphabetic order during a given season. The "gender" of the season's first storm also alternates year to year: the first storm of an odd-numbered year gets feminine name, while the first storm of an even-numbered year gets a masculine name. Six lists of names are prepared in advance, and each list is used once every six years. Five letters — "Q," "U," "X," "Y" and "Z" — are omitted in the Atlantic; only "Q" and "U" are omitted in the Eastern Pacific, so the format accommodates 21 or 24 named storms in a hurricane season. Names of storms may be retired by request of affected countries if they have caused extensive damage. The affected countries then decide on a replacement name of the same gender (and if possible, the same ethnicity) as the name being retired.

If there are more than 21 named storms in an Atlantic season or 24 named storms in an Eastern Pacific season, the rest are named as letters from the Greek alphabet: the 22nd storm is called "Alpha," the 23rd "Beta," and so on. This was first necessary during the 2005 season when the names Alpha, Beta, Gamma, Delta, Epsilon, and Zeta were all used. There is no precedent for a storm named with a Greek Letter causing enough damage to justify retirement; how this situation would be handled is unknown.

Further information: List of notable tropical cyclones

In the Central North Pacific region, the name lists are maintained by the Central Pacific Hurricane Center in Honolulu, Hawaii. Four lists of Hawaiian names are selected and used in sequential order without regard to year.

In the Western North Pacific, name lists are maintained by the WMO Typhoon Committee. Five lists of names are used, with each of the 14 nations on the Typhoon Committee submitting two names to each list. Names are used in the order of the countries' English names, sequentially without regard to year. Japan Meteorological Agency uses a secondary naming system in Western North Pacific that numbers a typhoon on the order it formed, resetting on December 31 of every year. The Typhoon Songda in September 2004 is internally called the typhoon number 18 and is recorded as the typhoon 0418 with 04 taken from the year.

The Australian Bureau of Meteorology maintains three lists of names, one for each of the Western, Northern and Eastern Australian regions. There are also Fiji region and Papua New Guinea region names.

The Seychelles Meteorological Service maintains a list for the Southwest Indian Ocean.

History of tropical cyclone naming

For several hundred years after Europeans arrived in the West Indies, hurricanes there were named after the saint's day on which the storm struck.

The practice of giving storms people's names was introduced by Clement Lindley Wragge, an Anglo-Australian meteorologist at the end of the 19th century. He used feminine names, the names of politicians who had offended him, and names from history and mythology.

During World War II, tropical cyclones were given feminine names, mainly for the convenience of the forecasters and in a somewhat ad hoc manner. For a few years afterwards, names from the Joint Army/Navy Phonetic Alphabet were used.

The modern naming convention came about in response to the need for unambiguous radio communications with ships and aircraft. As transportation traffic increased and meteorological observations improved in number and quality, several typhoons, hurricanes or cyclones might have to be tracked at any given time. To help in their identification, beginning in 1953 the practice of systematically naming tropical storms and hurricanes was initiated by the United States National Hurricane Center, and is now maintained by the WMO.

In keeping with the common English language practice of referring to inanimate objects such as boats, trains, etc., using the female pronoun "she," names used were exclusively feminine. The first storm of the year was assigned a name beginning with the letter "A", the second with the letter "B", etc. However, since tropical storms and hurricanes are primarily destructive, some considered this practice sexist. The National Weather Service responded to these concerns in 1979 with the introduction of masculine names to the nomenclature. It was also in 1979 that the practice of preparing a list of names before the season began. The names are usually of English, French or Spanish origin in the Atlantic basin, since these are the three predominant languages of the region where the storms typically form.

Renaming of tropical cyclones

In most cases, a tropical cyclone retains its name throughout its life. However, a tropical cyclone may be renamed in several occasions.

1. A tropical storm enters the southwestern Indian Ocean from the east

In the south Indian Ocean, RSMC la Reunion names a tropical storm once it crosses 90°E from the east, even though it has been named. In this case, the Joint Typhoon Warning Center (JTWC) will put two names together with a hyphen.

Examples: Bertie-Alvin (2005)

2. A tropical storm crosses from the Atlantic into the Pacific, or vice versa, before 2001

It was the policy of National Hurricane Center (NHC) to rename a tropical storm which crossed from Atlantic into Pacific, or vice versa.

Examples: Cesar-Douglas (1996), Joan-Miriam (1988)

In 2001, when Iris moved across Central America, NHC mentioned that Iris would retain its name if it regenerated in the Pacific. However, the Pacific tropical depression developed from the remnants of Iris was called Fifteen-E instead. The depression later became tropical storm Manuel.

NHC explained that Iris had dissipated as a tropical cyclone prior to entering the eastern North Pacific basin; the new depression was properly named Fifteen-E, rather than Iris.

In 2003, when Larry was about to move across Mexico, NHC attempted to provide greater clarity:

Up to now, there has been no tropical cyclone retaining its name during the passage from Atlantic to Pacific, or vice versa.

3. Uncertainties of the continuation

When the remnants of a tropical cyclone redevelop, the redeveloping system will be treated as a new tropical cyclone if there are uncertainties of the continuation, even though the original system may contribute to the forming of the new system.

Example: TD 10-TD 12 (2005)

4. Human faults

Sometimes, there may be human faults leading to the renaming of a tropical cyclone.

Example: Ken-Lola (1989)

Effects

The aftermath of Hurricane Katrina in Gulfport, Mississippi. Katrina was the costliest tropical cyclone in United States history.

A mature tropical cyclone can release heat at a rate upwards of 6x1014 watts [9]. Tropical cyclones on the open sea cause large waves, heavy rain, and high winds, disrupting international shipping and sometimes sinking ships. However, the most devastating effects of a tropical cyclone occur when they cross coastlines, making landfall. A tropical cyclone moving over land can do direct damage in four ways.

  • High winds - Hurricane strength winds can damage or destroy vehicles, buildings, bridges, etc. High winds also turn loose debris into flying projectiles, making the outdoor environment even more dangerous.
  • Storm surge - Tropical cyclones cause an increase in sea level, which can flood coastal communities. This is the worst effect, as cyclones claim 80% of their victims when they first strike shore.
  • Heavy rain - The thunderstorm activity in a tropical cyclone causes intense rainfall. Rivers and streams flood, roads become impassable, and landslides can occur.
  • Tornado activity - The broad rotation of a hurricane often spawns tornadoes. While these tornadoes are normally not as strong as their non-tropical counterparts, they can still cause tremendous damage.
Graphic illustrating storm surge

Often, the secondary effects of a tropical cyclone are equally damaging. They include:

  • Disease - The wet environment in the aftermath of a tropical cyclone, combined with the destruction of sanitation facilities and a warm tropical climate, can induce epidemics of disease which claim lives long after the storm passes. One of the most common post-hurricane injuries is stepping on a nail in storm debris, leading to a risk of tetanus or other infection. Infections of cuts and bruises can be greatly amplified by wading in sewage-polluted water.
  • Power outages - Tropical cyclones often knock out power to tens or hundreds of thousands of people (or occasionally millions if a large urban area is affected), prohibiting vital communication and hampering rescue efforts.
  • Transportation difficulties - Tropical cyclones often destroy key bridges, overpasses, and roads, complicating efforts to transport food, clean water, and medicine to the areas that need it.

Beneficial effects of tropical cyclones

Although cyclones take an enormous toll in lives and personal property, they may bring much-needed precipitation to otherwise dry regions. Hurricane Allen ended the Texas drought of 1980. Hurricane Camille averted drought conditions and ended water deficits along much of its path. Hurricane Floyd did the same thing in New Jersey in 1999. The destruction caused by Camille on the Gulf coast spurred redevelopment as well, greatly increasing local property values. On the other hand, disaster response officials point out that redevelopment encourages more people to live in clearly dangerous areas subject to future deadly storms (as shown by the effects of Hurricane Katrina). Of course, many former residents and businesses do relocate to inland areas away from the threat of future hurricanes as well.

Hurricanes also help to maintain global heat balance by moving warm, moist tropical air to the mid-latitudes and polar regions. James Lovelock has also hypothesised that by raising nutrients from the sea floor to surface layers of the ocean, hurricanes also increase biological activity in areas where life would be difficult through nutrient loss in the deeper reaches of the ocean.

Long term trends in cyclone activity

While the number of storms in the Atlantic has increased since 1995, there seems to be no signs of a global trend; the annual global number of tropical cyclones remains about 90 ± 10. [10].

Atlantic storms are certainly becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. This can to a large extent be attributed to the number of people living in susceptible coastal area, and massive development in the region since the last surge in Atlantic hurricane activity in the 1960s.

Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast often went unmeasured. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.

The number and strength of Atlantic hurricanes may undergo a 50-70-year cycle. Although more common since 1995, few above-normal hurricane seasons occurred during 1970-1994. Destructive hurricanes struck frequently from 1926-60, including many major New England hurricanes. A record 21 Atlantic tropical storms formed in 1933, only recently exceeded in 2005. Tropical hurricanes occurred infrequently during the seasons of 1900-1925; however, many intense storms formed 1870-1899. During the 1887 season, 19 tropical storms formed, of which a record 4 occurred after 1 November and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 1800s, including an 1821 storm that made a direct hit on New York City which some historical weather experts say may have been as high as Category 4 in strength.

These unusually active hurricane seasons predated satellite coverage of the Atlantic basin that now enables forecasters to see all tropical cyclones. Before the satellite era began in 1961, tropical storms or hurricanes went undetected unless a ship reported a voyage through the storm. The official record, therefore, probably misses many storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.

Global warming?

A common question is whether global warming can or will cause more frequent or more fierce tropical cyclones. So far, virtually all climatologists seem to agree that a single storm, or even a single season, cannot clearly be attributed to a single cause such as global warming or natural variation [11]. The question is thus whether a statistical trend in frequency or strength of cyclones exists. The U.S. National Oceanic and Atmospheric Administration says in their Hurricane FAQ that "it is highly unlikely that global warming has (or will) contribute to a drastic change in the number or intensity of hurricanes." [12].

Regarding strength, a similar conclusion was consensus until recently. This consensus is now questioned by K. Emanuel (2005) (Nature 436, 686–688, preprint). In this article, K. Emanuel states that the potential hurricane destructiveness, a measure which combines strength, duration, and frequency of hurricanes, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming." K. Emanuel further predicts "a substantial increase in hurricane-related losses in the twenty-first century".

Along similar lines, P.J. Webster et al. published an article in Science 309, 1844-1846 examining "changes in tropical cyclone number, duration, and intensity" over the last 35 years, a period where satellite data is available. The main finding is that while the number of cyclones "decreased in all basins except the North Atlantic during the past decade" there is a "large increase in the number and proportion of hurricanes reaching categories 4 and 5". I.e., while the number of cyclones decreased overall, the number of very strong cyclones increased.

Both Emanuel and Webster et al., consider the sea surface temperature as of key importance in the development of cyclones. The question then becomes: what caused the observed increase in sea surface temperatures? In the Atlantic, it could be due to the Atlantic Multidecadal Oscillation (AMO), a 50–70 year pattern of temperature variability. K. Emanuel, however, found the recent temperature increase was outside the range of previous oscillations. So, both a natural variation (such as the AMO) and global warming could have made contributions to the warming of the tropical Atlantic over the past decades, but an exact attribution is so far impossible to make. [13]

While Emanuel analyzes total annual energy dissipation, Webster et al. analyze the slightly less relevant percentage of hurricanes in the combined categories 4 and 5, and find that this percentage has increased in each of six distinct hurricane basins: North Atlantic, North East and North West Pacific, South Pacific, and North and South Indian. Because each individual basin may be subject to intra-basin oscillations similar to the AMO, any single-basin statistic remains open to question. But if the local oscillations are not synchronized by some as-yet-unidentified global oscillation, the independence of the basins allows joint statistical tests that are more powerful than any set of individual basin tests. Unfortunately Webster et al. do not undertake any such test.

Under the assumption that the six basins are statistically independent except for the effect of global warming, Stoft has carried out the obvious paired t-test and found that the null-hypothesis of no impact of global warming on the percentage of category 4 & 5 hurricanes can be rejected at the 0.1% level—there is only a 1 in 1000 chance of simultaneously finding the observed six increases in the cat-4&5 percentages. This statistic needs refining because the variables being tested are not normally distributed with equal variances, but it may provide the best evidence yet that the impact of global warming on hurricane intensity has been detected.

Notable cyclones

Tropical cyclones that cause massive destruction are fortunately rare, but when they happen, they can cause damage in the thousands of lives and the billions of dollars.

The deadliest tropical cyclone on record hit the densely populated Ganges Delta region of East Pakistan (now Bangladesh) on November 13, 1970, likely as a Category 3 tropical cyclone. It killed an estimated 500,000 people. The North Indian basin has historically been the deadliest, with three storms since 1900 killing over 100,000 people, each in Bangladesh. [14]

In the Atlantic basin, at least two storms have killed more than 10,000 people. Hurricane Mitch during the 1998 Atlantic hurricane season caused severe flooding and mudslides in Honduras, killing about 18,000 people and changing the landscape enough that entirely new maps of the country were needed. The Galveston Hurricane of 1900, which made landfall at Galveston, Texas as an estimated Category 4 storm, killed 8,000 to 12,000 people, and remains the deadliest natural disaster in the history of the United States. The deadliest Atlantic storm on record was the Great Hurricane of 1780, which killed about 22,000 people in the Antilles.

The relative sizes of Typhoon Tip, Tropical Cyclone Tracy, and the United States.

The most intense storm on record was Typhoon Tip in the northwestern Pacific Ocean in 1979, which had a minimum pressure of only 870 mbar and maximum sustained wind speeds of 190 mph (305 km/h). It weakened before striking Japan. Tip does not hold the record for fastest sustained winds in a cyclone alone; Typhoon Keith in the Pacific, and Hurricane Camille and Hurricane Allen in the North Atlantic currently share this record as well [15], although recorded wind speeds that fast are suspect, since most monitoring equipment is likely to be destroyed by such conditions.

Camille was the only storm to actually strike land while at that intensity, making it, with 190 mph (305 km/h) sustained winds and 210 mph (335 km/h) gusts, the strongest tropical cyclone of record to ever hit land. For comparison, these speeds are encountered at the center of a strong tornado, but Camille was much larger and long-lived than any tornado.

Typhoon Nancy in 1961 had recorded wind speeds of 213 mph (343 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the fastest storm on record. [16] Similarly, a gust caused by Typhoon Paka over Guam was recorded at 236 mph (380 km/h); however, this reading had to be discarded, since the anemometer was damaged by the storm. Had it been confirmed, this would be the strongest non-tornadic wind ever recorded at the Earth's surface. (The current record is held by a non-hurricane wind registering 231 mph (372 km/h) at Mount Washington in New Hampshire.) [17]

Tip was also the largest cyclone on record, with a circulation 1,350 miles (2,170 km) wide. The average tropical cyclone is only 300 miles (480 km) wide. The smallest storm on record, 1974's Cyclone Tracy, which devastated Darwin, Australia, was roughly 30 miles (50 km) wide. [18]

Hurricane Iniki in 1992 was the most powerful storm to strike Hawaii in recorded history, hitting Kauai as a Category 4 hurricane, killing six and causing $3 billion in damage.

The first recorded South Atlantic hurricane

On March 26, 2004, Cyclone Catarina became the first recorded South Atlantic hurricane. Previous South Atlantic cyclones in 1991 and 2004 reached only tropical storm strength. Hurricanes may have formed there prior to 1960 but were not observed until weather satellites began monitoring the Earth's oceans in that year.

A tropical cyclone need not be particularly strong to cause memorable damage; Tropical Storm Allison in June 2001 had its name retired for killing 41 people and causing over $5 billion damage in East Texas, even though it never became a hurricane; the damage from Allison was mostly due to flooding, not winds or storm surge. Hurricane Jeanne in 2004 was only a tropical storm when it made a glancing blow on Haiti, but the flooding and mudslides it caused killed over 3,000 people.

On August 29, 2005, Hurricane Katrina made landfall in Louisiana and Mississippi. The U.S. National Hurricane Center, in its August review of the tropical storm season stated that Katrina is probably the worst natural disaster in U.S. history. Its death toll is above 1300, mainly from flooding and the aftermath. It is also estimated to have caused an estimated $40 to $120 billion in damages. Before that, the most costly (in money, not human terms) storm had been 1992's Hurricane Andrew, which caused an estimated $25 billion in damage in Florida.


This page about Hurricanes includes information from a Wikipedia article.
Additional articles about Hurricanes
News stories about Hurricanes
External links for Hurricanes
Videos for Hurricanes
Wikis about Hurricanes
Discussion Groups about Hurricanes
Blogs about Hurricanes
Images of Hurricanes

Before that, the most costly (in money, not human terms) storm had been 1992's Hurricane Andrew, which caused an estimated $25 billion in damage in Florida. As an alt.* hierarchy group, alt.games.coh may not be available from some news servers. It is also estimated to have caused an estimated $40 to $120 billion in damages. As with any USENET group, flamewars can and do occur, sometimes lasting for days, but they are relatively seldom. Its death toll is above 1300, mainly from flooding and the aftermath. alt.games.coh is a low-traffic USENET newsgroup where City of Heroes is discussed. history. Flamewars seldom occur.

National Hurricane Center, in its August review of the tropical storm season stated that Katrina is probably the worst natural disaster in U.S. A variety of matters are discussed here in an informal setting, including discussions prohibited on the official forum. The U.S. The LiveJournal community for general discussion of City of Heroes-related issues is city_of_heroes. On August 29, 2005, Hurricane Katrina made landfall in Louisiana and Mississippi. Most of these are communities devoted to specific supergroups or servers. Hurricane Jeanne in 2004 was only a tropical storm when it made a glancing blow on Haiti, but the flooding and mudslides it caused killed over 3,000 people. Over sixty communities on the LiveJournal weblog site list City of Heroes as one of their interests.

A tropical cyclone need not be particularly strong to cause memorable damage; Tropical Storm Allison in June 2001 had its name retired for killing 41 people and causing over $5 billion damage in East Texas, even though it never became a hurricane; the damage from Allison was mostly due to flooding, not winds or storm surge. Fan sites listed on the portal are periodically reviewed by NCsoft to ensure that they are up and maintained. Hurricanes may have formed there prior to 1960 but were not observed until weather satellites began monitoring the Earth's oceans in that year. Any person may create a fan site and submit it to NCsoft for publication on the portal, pending review to ensure that the site meets with the guidelines for a fan site submission. Previous South Atlantic cyclones in 1991 and 2004 reached only tropical storm strength. NCsoft maintains a City of Heroes fan site portal on its official site. On March 26, 2004, Cyclone Catarina became the first recorded South Atlantic hurricane. Numerous City of Heroes fan sites exist with a wide variety of formats and purposes, including roleplaying sites and informational sites.

Hurricane Iniki in 1992 was the most powerful storm to strike Hawaii in recorded history, hitting Kauai as a Category 4 hurricane, killing six and causing $3 billion in damage. The European version of City of Heroes has its own separate official web board. [18]. The official web board is moderated to remove extreme antisocial behavior, discussion of client modification (such as map patches, skin modifications, or disabling certain sounds) prohibited by the EULA, and discussion of moderator decisions. The smallest storm on record, 1974's Cyclone Tracy, which devastated Darwin, Australia, was roughly 30 miles (50 km) wide. Reportedly only about 10% of the game's player base actually participates in these boards. The average tropical cyclone is only 300 miles (480 km) wide. However, there is also a very vocal faction of disgruntled gamers that produce flamewars and complaints which can cause would-be participants to stay away.

Tip was also the largest cyclone on record, with a circulation 1,350 miles (2,170 km) wide. Some find the presence of the developers, and their willingness to interact with and answer questions from players, to be laudable—especially in comparison to other MMORPGs, which tend not to have this type of developer availability. (The current record is held by a non-hurricane wind registering 231 mph (372 km/h) at Mount Washington in New Hampshire.) [17]. The value of this forum to the average player is a matter of debate. Had it been confirmed, this would be the strongest non-tornadic wind ever recorded at the Earth's surface. Currently, the primary forum moderator is CuppaJo. [16] Similarly, a gust caused by Typhoon Paka over Guam was recorded at 236 mph (380 km/h); however, this reading had to be discarded, since the anemometer was damaged by the storm. There are forums devoted to announcements, general issues, player guides, questions, suggestions, each archetype, each of the eleven game servers, City of Villains, and other topics.

Typhoon Nancy in 1961 had recorded wind speeds of 213 mph (343 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the fastest storm on record. This web board is run by Cryptic and NCSoft themselves, and frequented by various developers and customer service representatives (referred to by site regulars as "red names" because their usernames are highlighted in red on their forum posts) as well as players. For comparison, these speeds are encountered at the center of a strong tornado, but Camille was much larger and long-lived than any tornado. The official Internet forum for City of Heroes is the web board found at boards.cityofheroes.com. Camille was the only storm to actually strike land while at that intensity, making it, with 190 mph (305 km/h) sustained winds and 210 mph (335 km/h) gusts, the strongest tropical cyclone of record to ever hit land. Some prominent ones include:. Tip does not hold the record for fastest sustained winds in a cyclone alone; Typhoon Keith in the Pacific, and Hurricane Camille and Hurricane Allen in the North Atlantic currently share this record as well [15], although recorded wind speeds that fast are suspect, since most monitoring equipment is likely to be destroyed by such conditions. Many on-line communities exist for the discussion of City of Heroes.

It weakened before striking Japan. It should be noted that Time-Warner, owner of DC Comics see the CoH franchise as something which could promote the sales of its comics and doesn't consider the game to be a threat of any kind. The most intense storm on record was Typhoon Tip in the northwestern Pacific Ocean in 1979, which had a minimum pressure of only 870 mbar and maximum sustained wind speeds of 190 mph (305 km/h). Also, it's believed that Marvel's reputation of being trigger-happy with lawsuits worked against them. The deadliest Atlantic storm on record was the Great Hurricane of 1780, which killed about 22,000 people in the Antilles. Although details of the settlement are scarce, it's believed that Marvel's case was floundering because when they launched the suit, the examples of copyrighted characters being replicated by the games character creator cited by Marvel were found to have been made by Marvel's own employees, this led the judge to dismiss these specific examples and ordered that Marvel can never use similar evidence again. The Galveston Hurricane of 1900, which made landfall at Galveston, Texas as an estimated Category 4 storm, killed 8,000 to 12,000 people, and remains the deadliest natural disaster in the history of the United States. [3].

Hurricane Mitch during the 1998 Atlantic hurricane season caused severe flooding and mudslides in Honduras, killing about 18,000 people and changing the landscape enough that entirely new maps of the country were needed. Although the settlement has not been disclosed no changes will be made to the City of Heroes client. In the Atlantic basin, at least two storms have killed more than 10,000 people. As of December 14, 2005 all claims have been settled. [14]. Although Cherry Auction had not been directly selling the infringing items, the court found that it was vicariously or contributorally liable for the infringement. The North Indian basin has historically been the deadliest, with three storms since 1900 killing over 100,000 people, each in Bangladesh. Cherry Auction, Inc., a case in which a company that ran a flea market was successfully sued over intellectual property infringement because a vendor had been selling bootlegged records at that flea market.

It killed an estimated 500,000 people. v. The deadliest tropical cyclone on record hit the densely populated Ganges Delta region of East Pakistan (now Bangladesh) on November 13, 1970, likely as a Category 3 tropical cyclone. At least one has noted similarities to Fonovisa, Inc. Tropical cyclones that cause massive destruction are fortunately rare, but when they happen, they can cause damage in the thousands of lives and the billions of dollars. Many intellectual property analysts agree, but others have noted that trademark law is structured such that if Marvel believes their properties are being infringed upon, they have little choice but to file a lawsuit, regardless of its outcome. This statistic needs refining because the variables being tested are not normally distributed with equal variances, but it may provide the best evidence yet that the impact of global warming on hurricane intensity has been detected. Cryptic has replied that the lawsuit is frivolous.

Under the assumption that the six basins are statistically independent except for the effect of global warming, Stoft has carried out the obvious paired t-test and found that the null-hypothesis of no impact of global warming on the percentage of category 4 & 5 hurricanes can be rejected at the 0.1% level—there is only a 1 in 1000 chance of simultaneously finding the observed six increases in the cat-4&5 percentages. Others have pointed out that the EULA also includes a clause which gives ownership of created characters to Cryptic. do not undertake any such test. Some have noted that Cryptic already includes in its end-user license agreement (EULA) language forbidding the creation of copyrighted characters and has been known to delete or rename such characters. Unfortunately Webster et al. The suit seeks unspecified damages and an injunction to force the companies to stop making use of its characters. But if the local oscillations are not synchronized by some as-yet-unidentified global oscillation, the independence of the basins allows joint statistical tests that are more powerful than any set of individual basin tests. In November 2004, Marvel Comics filed a lawsuit against City of Heroes developer Cryptic Studios and publisher NCSoft alleging that the game not only allows, but actively promotes, the creation of characters whose copyrights and trademarks are owned by Marvel, and that Cryptic has intentionally failed to police these infringing characters.

Because each individual basin may be subject to intra-basin oscillations similar to the AMO, any single-basin statistic remains open to question. Other supplements (Paragon City source book, Monitor's Support Pack, Super-powered Operative's Dossier, etc.) will follow. analyze the slightly less relevant percentage of hurricanes in the combined categories 4 and 5, and find that this percentage has increased in each of six distinct hurricane basins: North Atlantic, North East and North West Pacific, South Pacific, and North and South Indian. It will be based on Eden Studio's Unisystem rules and the core book will be called Registration Manual. While Emanuel analyzes total annual energy dissipation, Webster et al. In another press release, Eden Studios, makers of RPGs based on Army of Darkness and Buffy the Vampire Slayer franchises, have been tapped to produce a tabletop role-playing game for City of Heroes. [13]. A recent 16 March 2005 press release announced Alderac Entertainment Group, maker of several collectible card games including Legend of the Five Rings, has been chosen to release a City of Heroes CCG.

So, both a natural variation (such as the AMO) and global warming could have made contributions to the warming of the tropical Atlantic over the past decades, but an exact attribution is so far impossible to make. Artist George Pérez provides the covers for the first three novels. Emanuel, however, found the recent temperature increase was outside the range of previous oscillations. A third novel, The Rikti War, written by Shane Hensley, is due out in August 2006 and will cover the epic transdimensional war between Earth and the Rikti homeworld. K. A second novel, The Freedom Phalanx, written by Robin Laws, is due for release in May 2006 and will detail the reformation of the hero team the Freedom Phalanx in the 1980s. The question then becomes: what caused the observed increase in sea surface temperatures? In the Atlantic, it could be due to the Atlantic Multidecadal Oscillation (AMO), a 50–70 year pattern of temperature variability. The novel chronicles the backstories of The Statesman and Lord Recluse, the central iconic characters in the City of Heroes and City of Villains franchises.

Both Emanuel and Webster et al., consider the sea surface temperature as of key importance in the development of cyclones. The first City of Heroes novel, The Web of Arachnos, by Robert Weinberg, was published by CDS Books (an imprint of the Perseus Publishing Group) in October 2005. I.e., while the number of cyclones decreased overall, the number of very strong cyclones increased. Some have criticized Cryptic for doing this, but many more feel that this is fair considering you never paid for the comic itself in the first place. The main finding is that while the number of cyclones "decreased in all basins except the North Atlantic during the past decade" there is a "large increase in the number and proportion of hurricanes reaching categories 4 and 5". For a small additional fee, you can still get the actual comics sent to your door. published an article in Science 309, 1844-1846 examining "changes in tropical cyclone number, duration, and intensity" over the last 35 years, a period where satellite data is available. It's belived Cryptic did this not only to compensate for the lack of additional monthly fees for playing both CoH and CoV, but also to solve the problem of comic books getting lost in the mail.

Webster et al. As of City of Villains launch, the free comic book deal switched from being an actual comic book being mailed to you to being able to access all existing CoH comic books on the company's website. Along similar lines, P.J. This was followed up by Dan Jurgens, who wrote the next three-issue arc named Bloodlines. Emanuel further predicts "a substantial increase in hurricane-related losses in the twenty-first century". Mark Waid wrote the first three issues of the new Top Cow comic.Starting with issue four, Troy Hickman (who received Eisner Award nominations for Best Short Story and Best Anthology for his Common Grounds comic from Top Cow Productions) wrote a three-issue story arc entitled Smoke and Mirrors. Emanuel states that the potential hurricane destructiveness, a measure which combines strength, duration, and frequency of hurricanes, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming." K. Unlike the previous volume, this series will follow the adventures of the city's most illustrious supergroup, the Freedom Phalanx led by The Statesman.

In this article, K. Beginning with the May 2005 issue, the comic book is published by Top Cow Productions, written by noted comic book writer Mark Waid, and illustrated by newcomer David Nakayama. Emanuel (2005) (Nature 436, 686–688, preprint). It followed the story of the heroes Apex, War Witch, and Horus, who were virtually unmentioned in the game until Issue #5, where War Witch is a trainer in Croatoa. This consensus is now questioned by K. It was written by one of the game's designers, Rick Dakan, art was by Brandon McKinney and coloring was by Moose Bauman. Regarding strength, a similar conclusion was consensus until recently. The comic's first volume ran 12 issues from May 2004 to April 2005.

National Oceanic and Atmospheric Administration says in their Hurricane FAQ that "it is highly unlikely that global warming has (or will) contribute to a drastic change in the number or intensity of hurricanes." [12]. At times, this rear section has also included comic strips by Scott Kurtz of the PvP webcomic and Tim Buckley of the Ctrl Alt Del webcomic. The U.S. The comic follows the adventures of fictional Paragon City heroes and ties into the game's plot development at times, as well as featuring a section devoted to fan art, fan fiction, and other miscellany in the back. The question is thus whether a statistical trend in frequency or strength of cyclones exists. North American subscribers to the game receive the City of Heroes monthly comic book in the mail; it is also available in some comic book stores. So far, virtually all climatologists seem to agree that a single storm, or even a single season, cannot clearly be attributed to a single cause such as global warming or natural variation [11]. As of March 2005 City of Heroes has around 150,000 subscribers worldwide (according to MMMGchart.com [2]).

A common question is whether global warming can or will cause more frequent or more fierce tropical cyclones. Once purchased, the player inputs a code from the card and their account is updated to allow as many months of play as the card is good for. The official record, therefore, probably misses many storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience. In addition to paying subscription fees via credit card, another option is pre-paid cards that are available at video game retailers. Before the satellite era began in 1961, tropical storms or hurricanes went undetected unless a ship reported a voyage through the storm. coh.ogaming.com has an article on why MMORPGs have recurring fees [1]. These unusually active hurricane seasons predated satellite coverage of the Atlantic basin that now enables forecasters to see all tropical cyclones. Portions of the subscription costs go to supporting a full-time "live" team, which develops additional content for the game; other portions support the significant server maintenance and bandwidth costs.

Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 1800s, including an 1821 storm that made a direct hit on New York City which some historical weather experts say may have been as high as Category 4 in strength. As in other MMORPGs, players must pay the publisher (NCSoft) a monthly fee to continue playing City of Heroes. During the 1887 season, 19 tropical storms formed, of which a record 4 occurred after 1 November and 11 strengthened into hurricanes. To be fair to newer players though, characters on canceled accounts may lose their names to players making new characters, however the character itself is left untouched and should the player return, if their name was taken they are allowed to give the character a new name, if the name was not taken they can still use it. Tropical hurricanes occurred infrequently during the seasons of 1900-1925; however, many intense storms formed 1870-1899. Also, the game is praised because your characters are NEVER deleted even if you leave the game for an extended period of time, unlike most MMORPGs where you character is fair game for deletion after a period of time (usually 3 months after you cancel your account). A record 21 Atlantic tropical storms formed in 1933, only recently exceeded in 2005. The communication level between players and developers is such that a player can actually private message Statesman, get their suggestion/question/complaint read, and possibly even responded to.

Destructive hurricanes struck frequently from 1926-60, including many major New England hurricanes. The development team will admit mistakes and also implement player suggestions. Although more common since 1995, few above-normal hurricane seasons occurred during 1970-1994. It also is often praised for having a development team that actually communicates with it's playerbase. The number and strength of Atlantic hurricanes may undergo a 50-70-year cycle. The launch of City of Heroes was widely reported as one of the most successful MMO launches in the history of the industry. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect. GameSpy went on to say that City of Heroes has the most flexible character creator to date of any MMORPG and has consistently given the update issues high marks.

The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. PC Gamer, Game Informer, GameSpy and several other industry magazines critically acclaimed City of Heroes for its foray into the superhero genre and gave the game top or near top scores across the board. Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast often went unmeasured. Computer Gaming World hailed the game saying "City of Heroes blows a superpowered gust of fresh air into an increasingly stale sword-and-sorcery MMO world" in August of 2004. This can to a large extent be attributed to the number of people living in susceptible coastal area, and massive development in the region since the last surge in Atlantic hurricane activity in the 1960s. As such, many fans of CoH feel that only Cryptic will be able to keep up a proper Superhero MMORPG whereas SOE and Microsoft will not. Atlantic storms are certainly becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. Entertainment, they have been criticized as not doing anything to help the already-troubled game, they are letting it get stagnant).

[10]. SOE has a repuatation for poorly handling licensed MMO's, such as Star Wars Galaxies (which has undergone several system revamps that have caused thousands of frustrated customers to leave each time) and Matrix Online (which SOE actually bought from Warner Bros. While the number of storms in the Atlantic has increased since 1995, there seems to be no signs of a global trend; the annual global number of tropical cyclones remains about 90 ± 10. There is also a DC Comics MMORPG that is being produced by Sony Online Entertainment. James Lovelock has also hypothesised that by raising nutrients from the sea floor to surface layers of the ocean, hurricanes also increase biological activity in areas where life would be difficult through nutrient loss in the deeper reaches of the ocean. Finally, the fact that the game will only be for XBox 360 is a heavy factor against it as it not only depends on a player to own the console, but also possibly be subscribed to XBox live Gold (Silver membership is free with ownership of the console and may very well be all that's required by Microsoft) and also have to pay an additional fee (which Marvel's development group would be collecting). Hurricanes also help to maintain global heat balance by moving warm, moist tropical air to the mid-latitudes and polar regions. However, it should be noted that currently the only alternatives that are in production are a Microsoft XBox 360-exclusive Marvel online game that may play more like a regular ORPG like Diablo, it should also be known that Microsoft has a shady history when it comes to MMORPG's, they've been held responsible for the death of Asheron's Call 2 and they have announced promising MMORPG's only to end up canceling them such as Mythica and True Fantasy Live Online.

Of course, many former residents and businesses do relocate to inland areas away from the threat of future hurricanes as well. Those who feel they have been slighted by changes in the game's mechanics claim they will jump ship at the first alternative game to be released. On the other hand, disaster response officials point out that redevelopment encourages more people to live in clearly dangerous areas subject to future deadly storms (as shown by the effects of Hurricane Katrina). Some players have pointed out that City of Heroes has thus far been able to escape penalties for its shortcomings because, as of now, they have the monopoly on super hero MMORPGs, although that may change as other contenders release similar games. The destruction caused by Camille on the Gulf coast spurred redevelopment as well, greatly increasing local property values. Statesman, in a response to a private message sent to him by a forum-goer regarding "SSOCSS" stated that this system is currently shelved for the time being. Hurricane Floyd did the same thing in New Jersey in 1999. This is understandable considering that Statesman had mentioned a special "Super Secret Out of Combat Skill System" in the past that has never materialized due to problems developing the system.

Hurricane Camille averted drought conditions and ended water deficits along much of its path. The lead developer stated that it wasn't mentioned before because he didn't want to release the info because they hadn’t worked out the exact system and didn't want to release false information. Hurricane Allen ended the Texas drought of 1980. They stated that ED had been in the works since March 2005, and that all changes to the game had been made with it in mind. Although cyclones take an enormous toll in lives and personal property, they may bring much-needed precipitation to otherwise dry regions. Eventually the developers posted the information on the CoH forums. They include:. The changes were originally posted on the City of Villains beta forums, however some testers who were angered by the changes attempted to leak the information on to the City of Heroes forums despite their Non-Disclosure Agreements.

Often, the secondary effects of a tropical cyclone are equally damaging. This is causing an even larger outcry than those on the changes in Issue 5. A tropical cyclone moving over land can do direct damage in four ways. A more recent criticism is against a change in the game's mechanics, called Enhancement Diversification (ED). However, the most devastating effects of a tropical cyclone occur when they cross coastlines, making landfall. Other players have also noted that the game does not incorporate the experience suggested in the in-game text written for mission descriptions and historical plaques, or the fictional world's history found on the game's website. Tropical cyclones on the open sea cause large waves, heavy rain, and high winds, disrupting international shipping and sometimes sinking ships. Some players say the game lacks an immersive feel and doesn't express fully the superhero comic book genre on which the game is based.

A mature tropical cyclone can release heat at a rate upwards of 6x1014 watts [9]. Other criticisms are more subjective. Example: Ken-Lola (1989). Other powers are so useful that they are considered essential for every character, such as Hasten, which allows powers to be reactivated more quickly after each use, and Stamina, which increases a character's endurance regeneration rate. Sometimes, there may be human faults leading to the renaming of a tropical cyclone. Some sets have powers that are rarely taken and are dismissed as useless. Human faults. As in all MMORPGs, there are calls to weaken, or nerf, these apparently overpowered sets.

4. Some players have criticized the game for being improperly balanced, with some power sets far outshining others. Example: TD 10-TD 12 (2005). City of Villains was released as both an expansion to City of Heroes and as a standalone game, a concept which has been dubbed "Expanshalone". When the remnants of a tropical cyclone redevelop, the redeveloping system will be treated as a new tropical cyclone if there are uncertainties of the continuation, even though the original system may contribute to the forming of the new system. The developer continually expands City of Heroes with free downloadable patches/updates. Uncertainties of the continuation. This was revealed to the players by Lead Developer Jack "Emmert" Statesman very early on in the City of Heroes beta test period.

3. Paragon City is a fictitious city located in Rhode Island. Up to now, there has been no tropical cyclone retaining its name during the passage from Atlantic to Pacific, or vice versa. Badges have become, for some players, a greatly needed push for more to do in the game than just fight. In 2003, when Larry was about to move across Mexico, NHC attempted to provide greater clarity:. As the game has expanded more badges have been added, as well as special "event" badges, the first was for Holloween of 2004, but more such events happen a couple times a year. NHC explained that Iris had dissipated as a tropical cyclone prior to entering the eastern North Pacific basin; the new depression was properly named Fifteen-E, rather than Iris. When a hero has collected specific groups of badges, he is granted an "Accolade"—a badge that includes additional special powers for the hero, such as a maximum health or endurance boost, or an attack.

The depression later became tropical storm Manuel. Plaques do not have to be read in any particular order. However, the Pacific tropical depression developed from the remnants of Iris was called Fifteen-E instead. Heroes can obtain certain badges by visiting and reading each plaque in a set, which are often scattered across two or more zones within the city. In 2001, when Iris moved across Central America, NHC mentioned that Iris would retain its name if it regenerated in the Pacific. Each plaque relates some historical fact about Paragon City's, its heroes', or the world's back story, and they are grouped into sets based on their subject matter. Examples: Cesar-Douglas (1996), Joan-Miriam (1988). Also added were a number of historical plaques, placed throughout Paragon City.

It was the policy of National Hurricane Center (NHC) to rename a tropical storm which crossed from Atlantic into Pacific, or vice versa. Thus, if a player finds the name of a badge to be well-suited to his character, or finds some in-game accomplishment especially significant, he can choose to title his character accordingly with that badge. A tropical storm crosses from the Atlantic into the Pacific, or vice versa, before 2001. These badges may be viewed by other players in the player information dialogue, and may also be worn to add the name of the badge as a title under a hero's publicly-displayed name. 2. These badges are obtained by visiting particular areas, achieving a certain security level, completing certain missions or sets of missions, defeating a quantity of specific types of foe, or special in-game achievements like taking a certain amount of damage or earning a certain amount of Influence. Examples: Bertie-Alvin (2005). In order to give the game more content, Cryptic introduced a system of collectible badges in its second content update to the game.

In this case, the Joint Typhoon Warning Center (JTWC) will put two names together with a hyphen. Influence can be spent to buy enhancements and inspirations, change the costume and adjust the difficulty level of missions. In the south Indian Ocean, RSMC la Reunion names a tropical storm once it crosses 90°E from the east, even though it has been named. Especially after a hero defeats a group of villains threatening a civilian on the streets of Paragon City, that civilian will run up to the hero and thank him by giving additional influence. A tropical storm enters the southwestern Indian Ocean from the east. For completing missions and defeating opponents heroes not only gain experience points, but also receive influence points. 1. Influence is the currency within City of Heroes.

However, a tropical cyclone may be renamed in several occasions. Special "gift" inspirations with a random ability (including temporary immunity from experience debt) have also been available upon occasion. In most cases, a tropical cyclone retains its name throughout its life. There is also one special inspiration, called ambrosia, used only for the Eden Trial. The names are usually of English, French or Spanish origin in the Atlantic basin, since these are the three predominant languages of the region where the storms typically form. The more powerful versions are less common. It was also in 1979 that the practice of preparing a list of names before the season began. In each of these types there are three specific inspirations, which help the affected area by 25%, 33%, and 50% (with rez, this refers to the amount of hp they have upon resurrecting).

The National Weather Service responded to these concerns in 1979 with the introduction of masculine names to the nomenclature. There is also a type that gives resistance and frees the hero who uses it from most status effects, usually referred to by the name of the weakest version, break free, and a type that resurrects a fallen hero, usually just called a rez or awaken. However, since tropical storms and hurricanes are primarily destructive, some considered this practice sexist. The types are generally referred to by the color they are represented by in the interface: blue (endurance), green (health), red (damage), yellow (accuracy), purple (defense) and the newest, orange (damage resistance). The first storm of the year was assigned a name beginning with the letter "A", the second with the letter "B", etc. There are usually 8 types of inspirations. In keeping with the common English language practice of referring to inanimate objects such as boats, trains, etc., using the female pronoun "she," names used were exclusively feminine. Characters gain the ability to hold more inspirations as they gain in level.

To help in their identification, beginning in 1953 the practice of systematically naming tropical storms and hurricanes was initiated by the United States National Hurricane Center, and is now maintained by the WMO. They can also be traded between player characters and bought from non-player characters. As transportation traffic increased and meteorological observations improved in number and quality, several typhoons, hurricanes or cyclones might have to be tracked at any given time. Inspirations can be used quickly and it is common to store some for more difficult battles. The modern naming convention came about in response to the need for unambiguous radio communications with ships and aircraft. Inspirations are quick powerups that many enemies drop randomly. For a few years afterwards, names from the Joint Army/Navy Phonetic Alphabet were used. An enhancement can only be combined twice with lower leveled enhancement, after that it can only be combined with a higher leveled enhancement.

During World War II, tropical cyclones were given feminine names, mainly for the convenience of the forecasters and in a somewhat ad hoc manner. The combination will result in a single enhancement one level higher than the highest leveled enhancement used. He used feminine names, the names of politicians who had offended him, and names from history and mythology. Two enhancements with the same level can always be combined without failing. The practice of giving storms people's names was introduced by Clement Lindley Wragge, an Anglo-Australian meteorologist at the end of the 19th century. Also the further apart the levels of the two enhancements are, the greater is the chance that the combination fails, thus losing the lower leveled enhancement. For several hundred years after Europeans arrived in the West Indies, hurricanes there were named after the saint's day on which the storm struck. To combine two enhancements they must have the same origin type and affected stat and one must be slotted.

The Seychelles Meteorological Service maintains a list for the Southwest Indian Ocean. All enhancements have the following characteristics:. There are also Fiji region and Papua New Guinea region names. Once an enhancement is put in, it can only be replaced by a different enhancement, or combined with another enhancement. The Australian Bureau of Meteorology maintains three lists of names, one for each of the Western, Northern and Eastern Australian regions. Each slot can hold exactly one enhancement. The Typhoon Songda in September 2004 is internally called the typhoon number 18 and is recorded as the typhoon 0418 with 04 taken from the year. Every power comes with one slot, and can have up to six slots attached to it.

Japan Meteorological Agency uses a secondary naming system in Western North Pacific that numbers a typhoon on the order it formed, resetting on December 31 of every year. At certain levels a character is given new enhancement slots to attach to a power. Names are used in the order of the countries' English names, sequentially without regard to year. Special enhancements can also can be earned by completing missions, trials and task forces. Five lists of names are used, with each of the 14 nations on the Typhoon Committee submitting two names to each list. Usually, heroes earn random enhancements and inspirations by defeating enemies, but they can also be bought at stores. In the Western North Pacific, name lists are maintained by the WMO Typhoon Committee. Enhancements and inspirations fill the roles of equipment and items in City Of Heroes, with enhancements being permanent and inspirations being temporary.

Four lists of Hawaiian names are selected and used in sequential order without regard to year. And finally the player chooses a name and can optionally write a background story to add some flavor to the character. In the Central North Pacific region, the name lists are maintained by the Central Pacific Hurricane Center in Honolulu, Hawaii. Next the actual avatar with its costume is created. There is no precedent for a storm named with a Greek Letter causing enough damage to justify retirement; how this situation would be handled is unknown. First the player selects an origin, an archetype and a primary and secondary power set. This was first necessary during the 2005 season when the names Alpha, Beta, Gamma, Delta, Epsilon, and Zeta were all used. Creating a character consists of several steps.

If there are more than 21 named storms in an Atlantic season or 24 named storms in an Eastern Pacific season, the rest are named as letters from the Greek alphabet: the 22nd storm is called "Alpha," the 23rd "Beta," and so on. Players can also form teams with other players to go on missions and fight villains together. The affected countries then decide on a replacement name of the same gender (and if possible, the same ethnicity) as the name being retired. Heroes can then enter 'Supergroup Mode' and change the colors and emblem of their normal avatar to those of their supergroup. Names of storms may be retired by request of affected countries if they have caused extensive damage. Supergroups pick a name, a motto, an emblem and two colors. Five letters — "Q," "U," "X," "Y" and "Z" — are omitted in the Atlantic; only "Q" and "U" are omitted in the Eastern Pacific, so the format accommodates 21 or 24 named storms in a hurricane season. Players can form supergroups (similar to other MMORPGs' guilds) reminiscent of classic comic book groups such as the X-Men or Justice League of America.

Six lists of names are prepared in advance, and each list is used once every six years. Teamwork is a large part of City of Heroes. The "gender" of the season's first storm also alternates year to year: the first storm of an odd-numbered year gets feminine name, while the first storm of an even-numbered year gets a masculine name. Several specially-designated Task Forces reward players with an opportunity to "respecify" their characters by choosing a different complement of superpowers or reassigning enhancements. In the Atlantic and Eastern North Pacific regions, feminine and masculine names are assigned alternately in alphabetic order during a given season. Upon completion, both Task Forces and Trials usually (but not always) provide all participants with a badge as well as a reward—either a Single-Origin or a special enhancement. The WMO's Regional Association IV Hurricane Committee selects the names for Atlantic Basin and central and eastern Pacific storms. Trials are similar to Task Forces but are usually shorter and more challenging; some share the team restrictions of a Task Force but others are taken as individual missions, though teams are still practically required.

Each year, the names of particularly destructive storms (if there were any) are "retired" and new names are chosen to take their place. In the case somebody is involuntarily disconnected, then he will return to the Task Force when connected. The lists are decided upon, depending on the regions, either by committees of the World Meteorological Organization (called primarily to discuss many other issues), or by national weather services involved in the forecasting of the storms. If a Task Force member voluntarily leaves the team while the Task Force is in progress, he is unable to rejoin it. These names are taken from lists which vary from region to region and are drafted a few years ahead of time. Once a Task Force has been started additional players will not be able to join the team. Storms reaching tropical storm strength (winds exceeding 17 metres per second, 38 mph, or 62 km/h) are given names, to assist in recording insurance claims, to assist in warning people of the coming storm, and to further indicate that these are important storms that should not be ignored. Task Forces always require a team, and consist of a series of linked missions that must be run to completion by that same team before its members may take on any additional missions.

The National Hurricane Center uses the data to evaluate conditions at landfall and to verify forecasts. For players who can devote a block of several hours to the game, two other types of missions with deeper storylines are available—the Task Force and the Trial. During landfall, the NOAA Hurricane Research Division compares and verifies data from reconnaissance aircraft (which includes wind speed data taken at flight level and from GPS dropwindsondes and stepped-frequency microwave radiometers) to wind speed data transmitted in real time from weather stations erected near or at the coast. Once a story arc is completed, the hero is rewarded with experience points, enhancements and for some story arcs, a badge. The two largest programs are the Florida Coastal Monitoring Program [7] and the Wind Engineering Mobile Instrumented Tower Experiment [8]. Sometimes, these story arcs affect the player hero directly as well. Recently, academic researchers have begun to deploy mobile weather stations fortified to withstand hurricane-force winds. These are a series of missions which form a larger story, often giving the player new insights into the history and mythos of Paragon City.

Radar plays a crucial role around landfall because it shows a storm's location and intensity minute by minute. Amid the missions, story arcs will emerge. As a storm approaches land, it can be observed by land-based Doppler radar. Since the release of the Issue 3 content update 'A Council of War', the player is now able to set the difficulty of the missions by visiting a special NPC, the Hero Corps Field Analyst. Tropical cyclones far from land are tracked by weather satellites capturing visible and infrared images from space, usually at half-hour to quarter-hour intervals. The difficulty level and number of the villains is adjusted according to the strength and number of the heroes grouped together. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare[6]. Heroes can venture into mission maps together if they form a team and choose a particular mission as the team's objective.

A new era in hurricane observation began when a remotely piloted Aerosonde, a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. It is usually possible to tell, by reading its description, whether a mission is timed before accepting it. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. Some missions may be completed at the hero's leisure, but others will have a set time limit which begins counting down as soon as the mission is accepted from the contact. The aircraft also launch GPS dropsondes inside the cyclone. Upon completion, heroes will be rewarded with an XP bonus, influence and occasionally a badge. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. As heroes venture further into the mission zone, they usually have to confront a Boss villain, rescue hostages, or find a particular clue.

The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engine turboprop cargo aircraft. When heroes reach approximately level 20, they begin to receive outdoor instanced missions set in fenced-off areas as well. In the Atlantic basin, these flights are regularly flown by US government hurricane hunters [5]. Missions, the City of Heroes equivalent of the quests typically found in other MMORPGs are given by non-playable characters (referred to as "contacts") and consist of either a "hunt" mission, where heroes are given the task of arresting a certain number of villains from one of the villain groups, or a private "instanced" mission map created solely for the player's team which is inhabited by a particular gang. It is however possible to take in-situ measurements, in real-time, by sending specially equipped reconnaissance flights into the cyclone. For instance, Circle of Thorns (a magic using villain group) members can always be found in the hazard zone of Perez Park. Even in these cases, real-time measurement taking is generally possible only in the periphery of the cyclone, where conditions are less catastrophic. Certain gangs are more likely to appear in different zones.

Surface level observations are generally available only if the storm is passing over an island or a coastal area, or it has overtaken an unfortunate ship. Groups of villains, all from the same gang and usually all with similar security levels, roam around areas of Paragon City. As they are a dangerous oceanic phenomenon, weather stations are rarely available on the site of the storm itself. There are a variety of different villain organisations and gangs in City of Heroes, each with unique attributes. Intense tropical cyclones pose a particular observation challenge. The Power Pools contain the aforementioned travel powers, as well as other generic, non-class specific powers such as Grant Invisibility, Provoke, Recall Friend, and Boxing. However, it has been suggested by some that we can change the course of a storm during its early stages of formation, (detailed by an article, Controlling Hurricanes, Scientific American, 2005), such as using satellite to alter the environmental conditions or, more realistically, spreading degradable film of oil over the ocean, which prevent water vapor from fueling the storm. While each archetype (listed below) has its own unique set of powers and abilities, all players have access to the powers from the ten Power Pools at level six.

These approaches all suffer from the same flaw: tropical cyclones are simply too large for any of them to be practical [4]. As heroes grow in level and accumulate more powers, they gain the ability to choose one of four traveling powers: teleportation, super speed, super jumping, and flight, each with its own advantages and disadvantages. Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing icebergs into the tropical oceans; dropping large quantities of ice into the eye at very early stages so that latent heat is absorbed by ice at the entrance (storm cell perimeter bottom) instead of heat energy being converted to kinetic energy at high altitudes vertically above; covering the ocean in a substance that inhibits evaporation; or blasting the cyclone apart with nuclear weapons. Heroes initially move around the zones by slowly jogging, sprinting or if they bought the deluxe edition of the game, sliding by using the Prestige Power Slide power. Today it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.[3]. Players can also travel to hazard or trial zones and the city's sewer system, which teem with large groups of enemies. The project was dropped after it was discovered that eyewall replacement cycles occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. In player terms, this means to go to a different area you have to either use the monorail operated by the Paragon Transit Authority or the roads that are guarded by the Police.

Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10 percent chance of making landfall within 48 hours. In story terms, the walls are used to prevent large scale attacks upon the city and to prevent high level enemies from entering low level areas. In an earlier episode, disaster struck when a hurricane east of Jacksonville, Florida, was seeded, promptly changed its course, and smashed into Savannah, Georgia[citation needed]. Paragon City, the city in which the game takes place, is divided into different zones by giant energy walls known as "War Walls". The winds of Hurricane Debbie dropped as much as 30 percent, but then regained their strength after each of two seeding forays. Enhancements are power-ups which players can socket onto powers to improve them permanently. It was thought that the seeding would cause supercooled water in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds. As a hero's security level increases by doing missions and defeating foes, they gain benefits such as more health, more powers, more slots for holding temporary power-ups called Inspirations, and more enhancement slots for powers.

In the 1960s and 1970s, the United States government attempted to weaken hurricanes in its Project Stormfury by seeding selected storms with silver iodide. Low level heroes always have trouble successfully damaging high level villains. In the Atlantic ocean, such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane-force wind speeds when they reach Europe as a European windstorm. A hero's chance to hit an enemy is determined by the difference between his level and the enemy's threat level. When a tropical cyclone reaches higher latitudes or passes over land, it may merge with weather fronts or develop into a frontal cyclone, also called extratropical cyclone. Players may choose to skip this tutorial if they like and head straight to one of two starting areas (Atlas Park and Galaxy City). Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane force) winds and drop several inches of rainfall. It is here they learn about the level system and how to determine which enemies to attack.

A tropical cyclone can cease to have tropical characteristics in several ways:. They start their adventure in a tutorial zone that teaches them how to play the game. For a list of notable and unusual landfalling hurricanes, see list of notable tropical cyclones. Players begin by using the game's extensive character creation system to select an archetype and Power Sets, design a unique costume, and write a back story for their hero. For emergency preparedness, actions should be timed from when a certain wind speed will reach land, not from when landfall will occur. . In fact, for a storm moving inland, the landfall area experiences half the storm before the actual landfall. Heroes must fight members of various gangs and organizations and complete quests given to them by NPCs in order to accumulate experience points (or "XP") and increase their security level.

Naturally, storm conditions may be experienced on the coast and inland well before landfall. In the game, players create superhero player characters who can team up with others to fight various villains in Paragon City and its surrounding areas. Officially, "landfall" is when a storm's center (the center of the eye, not its edge) reaches land. Six gratis major updates for City of Heroes have released since its launch, with more on the way for both City of Heroes and City of Villains. They attribute the lack of improvement in intensity forecasting to the complexity of tropical systems and an incomplete understanding of factors that affect their development. On October 31, 2005 the game's first sequel, City of Villains, was launched, allowing users to play as supervillains. But while track forecasts have become more accurate than 20 years ago, scientists say they are less skillful at predicting the intensity of tropical cyclones. The game was launched in North America on April 28, 2004 and in France, Germany, and the UK (by NCSoft Europe) on 4 February 2005 with Scandinavia, Italy, Spain, and Benelux to follow.

High-speed computers and sophisticated simulation software allow forecasters to produce computer models that forecast tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. City of Heroes (CoH) is a massively multiplayer online role-playing computer game based on the superhero comic book genre, developed by Cryptic Studios and published by NCSoft. With their understanding of the forces that act on tropical cyclones, and a wealth of data from earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. 6 months for £44.99 (£7.49 per month). Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system. 3 months for £23.99 (£7.99 per month). East Coast and in the Gulf of Mexico are eventually forced toward the northeast by high-pressure areas which move from west to east over North Africa. 1 month for £8.99.

Many tropical cyclones along the coast. 6 month for €64.99 (€10.83 per month). Such a track direction change is termed recurve. A hurricane moving from the Atlantic toward the Gulf of Mexico, for example, will recurve to the north and then northeast if it encounters winds blowing northwestward toward a high-pressure system passing over North Africa. 3 months for €34.99 (€11.66 per month). Finally, when a tropical cyclone moves into higher latitude, its general track around a high-pressure area can be deflected significantly by winds moving toward a low-pressure area. 1 month for €12.99. (Much of that is due to the conservation of angular momentum - air is drawn in from an area much larger than the cyclone such that the tiny angular velocity of that air will be magnified greatly when the distance to the storm center shrinks.). 12 months for $143.40 ($11.95 per month).

The Coriolis acceleration also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds. 6 months for $77.70 ($12.95 per month). Thus, tropical cyclones in the Northern Hemisphere, which commonly move west in the beginning, normally turn north (and are then usually blown east), and cyclones in the Southern Hemisphere are deflected south, if no strong pressure systems are counteracting the Coriolis Acceleration. 3 months for $41.85 ($13.95 per month). The southern part is pulled south, but since it is closer to the equator, the Coriolis force is a bit weaker there). 1 month for $14.99. in the north, the northern part of the cyclone has winds to the west, and the Coriolis force pulls them slightly north. IGN, Best of E3 2002 - Runner Up - Best MMOG.

This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents (i.e. Game Critics Awards, Nominee - Best Online Multiplayer - E3 2002. The earth's rotation also imparts an acceleration (termed the Coriolis Acceleration or Coriolis Effect). Game Revolution, Best of E3 2003 - Best Online Game. Also, in the area of the North Atlantic where hurricanes form, trade winds, which are prevailing westward-moving wind currents, steer tropical waves (precursors to tropical depressions and cyclones) westward from off the African coast toward the Caribbean and North America. Game Critics Awards, Best Online Multiplayer - E3 2003. Over the North Atlantic Ocean, tropical systems are steered generally westward by the east-to-west winds on the south side of the Bermuda High, a persistent high-pressure area over the North Atlantic. GameSpy, Editor’s Choice - May 28, 2004.

The major force affecting the track of tropical systems in all areas are winds circulating around high-pressure areas. Gamespy, Game of the Month - May 2004. The path of motion is referred to as a tropical cyclone's track.. Gamespot, Game of the Month - May 2004. That is, large-scale winds—the streams in the earth's atmosphere—are responsible for moving and steering tropical cyclones. IGN, Editor’s Choice - May 28, 2004. Although tropical cyclones are large systems generating enormous energy, their movements over the earth's surface are often compared to that of leaves carried along by a stream. Warcry, Best Expansion - City of Villains - E3 2004.

In British Shipping Forecasts, winds of force 12 on the Beaufort scale are described as "hurricane force.". Actiontrip, Editor’s Choice - June 3, 2004. However, two powerful extratropical cyclones that ravaged France, Germany, and the United Kingdom in December 1999, "Lothar" and "Martin", were named due to their unexpected power (equivalent to a category 1 or 2 hurricane). The Adrenaline Vault, Seal of Excellence - June 15, 2004. These European windstorms can generate hurricane-force winds but are not given individual names. Loadedinc, Hot Property Award - June 30, 2004. In the United Kingdom and Europe, some severe northeast Atlantic cyclonic depressions are referred to as "hurricanes," even though they rarely originate in the tropics. Game Informer, PC Game of the Month - July 2004 Issue.

Although subtropical storms rarely attain hurricane-force winds, they may become tropical in nature as their core warms. Computer Gaming World, Editor's Choice - August 2004. They can form in a wide band of latitude, from the equator to 50°. Computer Games Magazine, Editor’s Choice - August 2004 Issue. A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. Games Magazine, Game of the Year 2004. Extratropical cyclones can also be dangerous because their low-pressure centers cause powerful winds. Wargamer, Award for Excellence - October 14, 2004.

From space, extratropical storms have a characteristic "comma-shaped" cloud pattern. Billboard 2004 Digital Entertainment Conference & Awards, Multiplayer Game of the Year - November 5, 2004. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses; more rarely, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. Billboard 2004 Digital Entertainment Conference & Awards, PC or Console Game of the Year - November 5, 2004. An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. GameSpy.com, PC Games of the Year - December 24, 2004. Several of these relate to the formation or dissipation of tropical cyclones. Spike TV, MMORPG Game of the Year - December 15, 2004.

Many other forms of cyclone can form in nature. Computer Gaming World, MMORPG Game of the Year - February 2005. weather service defines sustained winds based on 1-minute average speed measured about 10 meters (33 ft) above the surface. Hamidon enhancements are only level 50. The U.S. For example, a level 6 character can use enhancements level 3 through 9. The definition of sustained winds recommended by the World Meteorological Organization (WMO) and used by most weather agencies is that of a 10-minute average. The difference of the level of the enhancement and the character must be within 3.

The Joint Typhoon Warning Center classifies typhoons with wind speeds of at least 150 mi/h (67 m/s or 241 km/h, equivalent to a strong Category 4 storm) as Super Typhoons. Level is a number on the enhancement that determines what security level a character can be to use it. The National Hurricane Center classifies hurricanes of Category 3 and above as Major Hurricanes. Hamidon, Crystal Titan, and Hydra enhancements can be used by any origin and give a 33% boost in two or three different categories (for example, it might do both damage and accuracy). In fact, tropical systems of less than hurricane strength can produce significant damage and human casualties, especially from flooding and landslides. Single Origin enhancements can be used by only one origin and give about a 33% boost. For instance, a Category 2 hurricane that strikes a major urban area will likely do more damage than a large Category 5 hurricane that strikes a mostly rural region. Dual Origin enhancements can be used by only two origins and give about a 16.5% boost.

Lower-category storms can inflict greater damage than higher-category storms, depending on factors such as local terrain and total rainfall. Training enhancements can be used by any origin and give about an 8.3% boost. The rankings are not absolute in terms of effects. Origin type determinates which origins can use a specific enhancement and how large its boost is:

    . A Category 1 storm has the lowest maximum winds, a Category 5 hurricane has the highest. Hamidon enhancements affect two or three stats. Hurricanes are ranked according to their maximum winds using the Saffir-Simpson Hurricane Scale. For example, the damage enhancements increase damage, but the endurance cost enhancements decrease the endurance cost.

    Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger. This can either increase or decrease the affected stat. the maximum winds die off a bit and the central pressure goes up). Stat affected is labeled on the enhancement, and shows what stat of a power it will boost. During this phase, the tropical cyclone is weakening (i.e. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum.

    When cyclones reach peak intensity they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 5 to 15 miles. Eyewall replacement cycles naturally occur in intense tropical cyclones. Intense, mature hurricanes can sometimes exhibit an inward curving of the eyewall top that resembles a football stadium: this phenomenon is thus sometimes referred to as stadium effect. Maximum sustained winds in the strongest tropical cyclones have been measured at more than 85 m/s (165 knots, 190 mph, 305 km/h).

    The direction of the cyclonic circulation depends on the hemisphere; it is counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere. Bands or arms may extend over great distances as clouds are drawn toward the cyclone. The circulation of clouds around a cyclone's center imparts a distinct spiral shape to the system. Surrounding the eye is the eyewall, an area about 10 to 50 miles (16 to 80 kilometers) wide in which the strongest thunderstorms and winds circulate around the storm's center.

    The eye is often visible in satellite images as a small, circular, cloud-free spot. At hurricane and typhoon intensity, a tropical cyclone tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of the circulation. Government weather services assign first names to systems that reach this intensity (thus the term named storm). At this point, the distinctive cyclonic shape starts to develop, though an eye is usually not present.

    A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 and 33 meters per second (34–63 knots, 39–73 mph, or 62–117 km/h). It is already becoming a low-pressure system, however, hence the name "depression". It has no eye, and does not typically have the spiral shape of more powerful storms. A tropical depression is an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of less than 17 metres per second (33 knots, 38 mph, or 62 km/h).

    Tropical cyclones are classified into three main groups: tropical depressions, tropical storms, and a third group whose name depends on the region. A strong tropical cyclone consists of the following components. The following areas spawn tropical cyclones only very rarely. There are seven main basins of tropical cyclone formation:.

    It is estimated that such conditions occur only once every 400 years. A combination of a pre-existing disturbance, upper level divergence and a monsoon-related cold spell led to Typhoon Vamei at only 1.5 degrees north of the equator in 2001. Hurricane Ivan of 2004 developed within 10 degrees of the equator. These conditions are extremely rare, and such storms are believed to form at most once per century.

    However, it is possible for tropical cyclones to form within this boundary if there is another source of initial rotation. Because the Coriolis effect initiates and maintains tropical cyclone rotation, such cyclones almost never form or move within about 10 degrees of the equator [2], where the Coriolis effect is weakest. Nearly all of them form between 10 and 30 degrees of the equator and 87% form within 20 degrees of it. Most tropical cyclones form in a worldwide band of thunderstorm activity called the Intertropical convergence zone (ITCZ).

    Worldwide, an average of 80 tropical cyclones form each year. Southern Hemisphere activity peaks in mid-February to early March. In the Southern Hemisphere, tropical cyclone activity begins in late October and ends in May. In the North Indian basin, storms are most common from April to December, with peaks in May and November.

    The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and a peak in early September. The Northeast Pacific has a broader period of activity, but in a similar timeframe to the Atlantic. The statistical peak of the North Atlantic hurricane season is September 10. In the North Atlantic, a distinct hurricane season occurs from June 1 to November 30, sharply peaking from late August through September.

    However, each particular basin has its own seasonal patterns. Worldwide, tropical cyclone activity peaks in late summer when water temperatures are warmest. These include:. Only specific weather disturbances can result in tropical cyclones.

    Tropical cyclones occasionally form despite not meeting these conditions. Five factors are necessary to make tropical cyclone formation possible:. The formation of tropical cyclones is the topic of extensive ongoing research, and is still not fully understood. The high cirrus clouds may be the first signs of an approaching hurricane.

    This outflow produces high, thin cirrus clouds that spiral away from the center. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine. While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. Scientists at the National Center for Atmospheric Research estimate that a hurricane releases heat energy at the rate of 50 to 200 trillion watts -- about the amount of energy released by exploding a 10-megaton nuclear bomb every 20 minutes [1].

    As a result, when a tropical cyclone passes over land, its strength diminishes rapidly. The evaporation of this moisture is accelerated by the high winds and reduced atmospheric pressure in the storm, resulting in a positive feedback loop. In order to continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the atmospheric moisture needed. By contrast, mid-latitude cyclones, for example, draw their energy mostly from pre-existing horizontal temperature gradients in the atmosphere.

    Condensation as a driving force is what primarily distinguishes tropical cyclones from other meteorological phenomena, and because this is strongest in a tropical climate, this defines the initial domain of the tropical cyclone. If the right conditions persist and allow it to create a feedback loop by maximizing the energy intake possible, for example, such as high winds to increase the rate of evaporation, they can combine to produce the violent winds, incredible waves, torrential rains, and floods associated with this phenomenon. The factors to form a tropical cyclone include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. The orbital revolution of the Earth causes the system to spin, an effect known as the Coriolis force, giving it a cyclone characteristic and affecting the trajectory of the storm.

    Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. This gives rise to factors that give the system enough energy to be self-sufficient and cause a positive feedback loop where it can draw more energy as long as the source of heat, warm water, remains. Continued condensation leads to higher winds, continued evaporation, and continued condensation, feeding back into itself. Therefore, a tropical cyclone can be thought of as a giant vertical heat engine supported by mechanics driven by physical forces such as the rotation and gravity of the Earth.

    Its primary energy source is the release of the heat of condensation from water vapor condensing at high altitudes, the heat ultimately derived from the sun. Structurally, a tropical cyclone is a large, rotating system of clouds, wind and thunderstorms. [citation needed]. The word cyclone is from the Greek "κύκλος", meaning "circle." An Egyptian word Cykline meaning to "to spin" has been cited as a possible origin.

    The word hurricane is derived from the name of a native Caribbean Amerindian storm god, Huracan, via Spanish huracán. See tuphōn for more information. Portuguese tufão is also related to typhoon. The word typhoon has two possible origins:.

    There are many regional names for tropical cyclones, including Bagyo in the Philippines and Taino in Haiti. Terms used in weather reports for tropical cyclones that have surface winds over 64 knots (73.6 mph) or 32 m/s vary by region:. . While they can be highly destructive, tropical cyclones are an important part of the atmospheric circulation system, which moves heat from the equatorial region toward the higher latitudes.

    In meteorology, a tropical cyclone (also referred to as a tropical depression, tropical storm, typhoon, or hurricane depending on strength and geographical context) is a type of low pressure system which generally forms in the tropics. Transportation difficulties - Tropical cyclones often destroy key bridges, overpasses, and roads, complicating efforts to transport food, clean water, and medicine to the areas that need it. Power outages - Tropical cyclones often knock out power to tens or hundreds of thousands of people (or occasionally millions if a large urban area is affected), prohibiting vital communication and hampering rescue efforts. Infections of cuts and bruises can be greatly amplified by wading in sewage-polluted water.

    One of the most common post-hurricane injuries is stepping on a nail in storm debris, leading to a risk of tetanus or other infection. Disease - The wet environment in the aftermath of a tropical cyclone, combined with the destruction of sanitation facilities and a warm tropical climate, can induce epidemics of disease which claim lives long after the storm passes. While these tornadoes are normally not as strong as their non-tropical counterparts, they can still cause tremendous damage. Tornado activity - The broad rotation of a hurricane often spawns tornadoes.

    Rivers and streams flood, roads become impassable, and landslides can occur. Heavy rain - The thunderstorm activity in a tropical cyclone causes intense rainfall. This is the worst effect, as cyclones claim 80% of their victims when they first strike shore. Storm surge - Tropical cyclones cause an increase in sea level, which can flood coastal communities.

    High winds also turn loose debris into flying projectiles, making the outdoor environment even more dangerous. High winds - Hurricane strength winds can damage or destroy vehicles, buildings, bridges, etc. Such weakening is generally temporary unless it meets other conditions above. An outer eye wall forms (typically around 50 miles from the center of the storm), choking off the convection toward the inner eye wall.

    These storms are extratropical cyclones. This does not necessarily mean the death of the storm, but the storm will lose its tropical characteristics. It enters colder waters. (Such, however, can strengthen the non-tropical system as a whole.).

    It can be weak enough to be consumed by another area of low pressure, disrupting it and joining to become a large area of non-cyclonic thunderstorms. It experiences wind shear, causing the convection to lose direction and the heat engine to break down. Without warm surface water, the storm cannot survive. It remains in the same area of ocean for too long, drawing heat off of the ocean surface until it becomes too cool to support the storm.

    However, many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall which can lead to deadly floods and mudslides. If a storm is over mountains for even a short time, it can rapidly lose its structure. There is, however, a chance they could regenerate if they manage to get back over open warm water. Most strong storms lose their strength very rapidly after landfall, and become disorganized areas of low pressure within a day or two.

    It moves over land, thus depriving it of the warm water it needs to power itself, and quickly loses strength. Tropical cyclones owe this unique characteristic to the warm core at the center of the storm. Winds at the surface are strongly cyclonic, weaken with height, and eventually reverse themselves. Outflow: The upper levels of a tropical cyclone feature winds headed away from the center of the storm with an anticyclonic rotation.

    The heaviest wind damage occurs where a hurricane's eyewall passes over land. Eyewall: A band around the eye of greatest wind speed, where clouds reach highest and precipitation is heaviest. In weaker cyclones, the CDO covers the circulation center, resulting in no visible eye. The eye is normally circular in shape, and may range in size from 8 km to 200 km (5 miles to 125 miles) in diameter.

    Eyes are home to the coldest temperatures of the storm at the surface, and the warmest temperatures at the upper levels. Weather in the eye is normally calm and free of clouds (however, the sea may be extremely violent). Eye: A strong tropical cyclone will harbor an area of sinking air at the center of circulation. The classic hurricane contains a symmetrical CDO, which means that it is perfectly circular and round on all sides.

    This contains the eye wall, and the eye itself. Central Dense Overcast (CDO): The Central Dense Overcast is a dense shield of very intense thunderstorm activity that make up the inner portion of the hurricane. Thus, at any given altitude (except close to the surface where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings. This heat is distributed vertically, around the center of the storm.

    Warm core: Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation as moist air is carried upwards and its water vapor condenses. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level. Surface low: All tropical cyclones rotate around an area of low atmospheric pressure near the Earth's surface. The Great Lakes A storm system that appeared similar to a tropical cyclone formed in 1996 on Lake Huron it formed an eye and could have breifly been sub-tropical.

    It formed from a thunderstorm formation in Borneo that moved into the South China Sea. It caused flooding in southern Malaysia and some damage in Singapore. However, in December 2001, Typhoon Vamei formed in the Southern South China Sea and made landfall in Malaysia. Areas within ten degrees laditude of the equator do not experience a significant coriolis force, a vital ingredient in tropical cyclone formation.

    Southern South China Sea Tropical cyclones normally do not develop in the Southern South China Sea due to its close proximity to the equator. Australia: SE Indian Basin includes the eastern part of the Indian ocean and the northern and western part of the Australian basin. Australia: SW Pacific Basin includes the eastern part of Australia and the Fiji area. before being transformed into an extratropical low or absorbed into other systems of low pressure.

    Vince's origin was the northeasternmost in the eastern Atlantic ever recorded, and Vince was the first storm in recorded history to reach the Iberian Peninsula as a tropical cyclone, i.e. Northeastern Atlantic Ocean: In October 2005, Hurricane Vince formed near Madeira, then moved northeastward, passing south of the Portuguese south coast, and made landfall in southwestern Spain as a tropical depression. However, there is debate on whether these storms were tropical in nature. Such cyclones formed in September 1947, September 1969, January 1982, September 1983, and January 1995.

    Mediterranean Sea: Storms which appear similar to tropical cyclones in structure sometimes occur in the Mediterranean basin. They affect the islands of Polynesia in exceptional instances. Most of the storms that enter this region formed farther west in the Southwest Pacific. Eastern South Pacific: Tropical cyclone formation is rare in this region; when they do form, it is frequently linked to El Niño episodes.

    However, this region is commonly frequented by tropical cyclones that form in the much more favorable Eastern North Pacific Basin. Central North Pacific: Shear in this area of the Pacific Ocean severely limits tropical development. The January storm is thought to have reached tropical storm intensity based on scatterometre winds. However, three tropical cyclones have been observed here — a weak tropical storm in 1991 off the coast of Africa, Cyclone Catarina (sometimes also referred to as Aldonça), which made landfall in Brazil in 2004 at Category 1 strength, and a smaller storm in January 2004, east of Salvador, Brazil.

    South Atlantic Ocean: A combination of cooler waters, the lack of an ITCZ, and wind shear makes it very difficult for the South Atlantic to support tropical activity. Cyclones forming here impact Madagascar, Mozambique, Mauritius, and Kenya, and these nations issue forecasts and warnings for the basin. Southwestern Indian Ocean: This basin is the least understood, due to a lack of historical data. Southeastern Indian Ocean: Tropical activity in this region affects Australia and Indonesia, and is forecast by those nations.

    Rarely, a tropical cyclone formed in this basin will affect the Arabian Peninsula. Nations affected by this basin include India, Bangladesh, Sri Lanka, Thailand, Myanmar, and Pakistan, and all of these countries issue regional forecasts and warnings. Hurricanes which form in this basin have historically cost the most lives — most notably, the 1970 Bhola cyclone killed 200,000. This basin's season has an interesting double peak; one in April and May before the onset of the monsoon, and another in October and November just after.

    Northern Indian Ocean: This basin is divided into two areas, the Bay of Bengal and the Arabian Sea, with the Bay of Bengal dominating (5 to 6 times more activity). South Western Pacific Ocean: Tropical activity in this region largely affects Australia and Oceania, and is forecast by Australia and Papua New Guinea. In the U.S., the Central Pacific Hurricane Center is responsible for forecasting the western part of this area while the National Hurricane Center is responsible for the eastern part. Storms that form here can affect western Mexico, Hawaii, northern Central America, and on extremely rare occasions, California.

    Eastern North Pacific Ocean: This is the second most active basin in the world, and the most dense (a large number of storms for a small area of ocean). National meteorology organizations and the Joint Typhoon Warning Center (JTWC) are responsible for issuing forecasts and warnings in this basin. The eastern coasts of Taiwan and Philippines also have the highest tropical cyclone landfall frequency in the world. This is by far the most active basin, accounting for one-third of all tropical cyclone activity in the world.

    Western North Pacific Ocean: Tropical storm activity in this region frequently affects China, Japan, the Philippines, and Taiwan, but also many other countries in South-East Asia, such as Vietnam, South Korea and Indonesia, plus numerous Oceanian islands. Many of the more intense Atlantic storms are Cape Verde-type hurricanes, which form off the west coast of Africa near the Cape Verde islands. The coast of Atlantic Canada receives hurricane landfalls on rare occasion, such as Hurricane Juan in 2003. Gulf Coast and occasionally New Jersey, New York and New England (usually hurricanes weaken to tropical storms before they reach these northern regions).

    Additionally, they can hit the coast of the U.S., especially Florida, North Carolina, the U.S. Hurricanes that strike Mexico, Central America, and Caribbean island nations, often do intense damage, as hurricanes are deadlier over warmer water. National Hurricane Center (NHC) based in Miami, Florida, issues forecasts for storms for all nations in the region; the Canadian Hurricane Centre, based in Halifax, Nova Scotia, also issues forecasts and warnings for storms expected to affect Canadian territory and waters. The U.S.

    Venezuela, the south-east of Canada and Atlantic "Macaronesian" islands are also occasionally affected. The United States Atlantic coast, Mexico, Central America, the Caribbean Islands and Bermuda are frequently affected by storms in this basin. The average is about ten. Tropical cyclone formation here varies widely from year to year, ranging from over twenty to one per year.

    North Atlantic Basin: The most-studied of all tropical basins, it includes the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. If a low level circulation forms under this convection, it may develop into a tropical cyclone. Decaying frontal boundaries may occasionally stall over warm waters and produce lines of active convection. A warm-core tropical cyclone may result when one of these (on occasion) works down to the lower levels and produces deep convection.

    Tropical upper tropospheric troughs, which are cold-core upper level lows. A similar phenomenon to tropical waves are West African disturbance lines, which are squally lines of convection that form over Africa and move into the Atlantic. Most tropical cyclones form from these. This often assists in the development of thunderstorms, which can develop into tropical cyclones.

    Tropical waves, or easterly waves, which, as mentioned above, are westward moving areas of convergent winds. High wind shear can break apart the vertical structure of a tropical cyclone. Low vertical wind shear (change in wind speed or direction over height). (2004's Hurricane Ivan was the strongest storm to form closer than 10 degrees from the equator; it started forming at 9.7 degrees north.).

    A distance of approximately 10 degrees or more from the equator, so that the Coriolis effect is strong enough to initiate the cyclone's rotation. This is most frequently provided by tropical waves—non-rotating areas of thunderstorms that move through tropical oceans. A pre-existing weather disturbance. Temperature in the atmosphere must decrease quickly with height, and the mid-troposphere must be relatively moist.

    Upper-atmosphere conditions conducive to thunderstorm formation. The moisture in the air above the warm water is the energy source for tropical cyclones. Sea surface temperatures above 26.5 degrees Celsius (79.7 degrees Fahrenheit) to at least a depth of 50 meters (164 feet). From Urdu, Persian or Arabic ţūfān (طوفان) < Greek tuphōn (Τυφών).

    The first record of the character 颱 appeared in 1685's edition of Summary of Taiwan 臺灣記略). (The Chinese term as 颱風 táifēng, and 台風 taifu in Japanese, has an independent origin traceable variously to 風颱, 風篩 or 風癡 hongthai, going back to Song 宋 (960-1278) and Yuan 元(1260-1341) dynasties. From the Chinese 大風 (daaih fūng (Cantonese); dà fēng (Mandarin)) which means "great wind". Cyclone (unofficially): South Atlantic Ocean.

    Tropical cyclone: Southwest Indian Ocean and the South Pacific east of 160°E. Severe cyclonic storm: North Indian Ocean. Severe tropical cyclone: Southwest Pacific west of 160°E and the southeast Indian Ocean east of 90°E. Typhoon: Northwest Pacific west of the dateline.

    Hurricane: Atlantic basin and North Pacific Ocean east of the dateline.

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