|Formation and naming|
|Development - Structure|
Naming - Seasonal lists - Full list
Watches and warnings
Storm surge - Notable storms
Retired hurricanes (Atlantic - Pacific)
|Climatology and tracking|
|Basins - RSMCs - TCWCs - Scales|
Observation - Rainfall forecasting - Rainfall climatology
|Part of the Nature series: Weather|
A tropical cyclone is a meteorological term for a storm system characterized by a low pressure system center and thunderstorms that produces strong wind and flooding rain. A tropical cyclone feeds on the heat released when moist air rises and the water vapor it contains condenses. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.
The adjective "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their formation in Maritime Tropical air masses. The noun "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere. Depending on their location and strength, tropical cyclones are referred to by various other names, such as hurricane, typhoon, tropical storm, cyclonic storm, and tropical depression.
While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and damaging storm surge. They develop over large bodies of warm water, and lose their strength if they move over land. This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 25 mi (40 km) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions. They also carry heat and energy away from the tropics and transport it towards temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere, and to maintain a relatively stable and warm temperature worldwide.
Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates.
- See also: Eye (cyclone)
BandingRainbands are bands of showers and thunderstorms that spiral cyclonically toward the storm center. High wind gusts and heavy downpours often occur in individual rainbands, with relatively calm weather between bands. Tornadoes often form in the rainbands of landfalling tropical cyclones. Intense annular tropical cyclones are distinctive for their lack of rainbands; instead, they possess a thick circular area of disturbed weather around their low pressure center. While all surface low pressure areas require divergence aloft to continue deepening, the divergence over tropical cyclones is in all directions away from the center. The upper levels of a tropical cyclone feature winds directed away from the center of the storm with an anticyclonic rotation, due to the Coriolis effect. Winds at the surface are strongly cyclonic, weaken with height, and eventually reverse themselves. Tropical cyclones owe this unique characteristic to requiring a relative lack of vertical wind shear to maintain the warm core at the center of the storm.
Eye and inner coreA strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into an eye. Weather in the eye is normally calm and free of clouds, though the sea may be extremely violent. The eye is normally circular in shape, and may range in size from 3 to 370 km (2–230 miles) in diameter. Intense, mature tropical cyclones can sometimes exhibit an inward curving of the eyewall's top, making it resemble a football stadium; this phenomenon is thus sometimes referred to as the stadium effect.
There are other features that either surround the eye, or cover it. The central dense overcast is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone; in weaker tropical cyclones, the CDO may cover the center completely. The eyewall is a circle of strong thunderstorms that surrounds the eye; here is where the greatest wind speeds are found, where clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land. Associated with eyewalls are eyewall replacement cycles, which occur naturally 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 10–25 km (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 angular momentum. During this phase, the tropical cyclone weakens (i.e., the maximum winds die off somewhat and the central pressure goes up), but eventually the outer eyewall replaces the inner one completely. The storm can be of the same intensity as it was previously or, in some cases, it can be even stronger after the eyewall replacement cycle. Even if the cyclone is weaker at the end of the cycle, the storm may strengthen again as it builds a new outer ring for the next eyewall replacement.
SizeThe size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed isobar. If the radius is less than two degrees of latitude (120 nmi, 222 km), then the cyclone is "very small" or a "midget." Radii of 2–3 degrees (120–180 nmi, 222–333 km) are considered "small." Radii between 3 and 6 latitude degrees (180–360 nmi, 333–666 km) are considered "average sized." Tropical cyclones are considered "large" when the closed isobar radius is 6–8 degrees of latitude (360–480 nmi, 666–888 km), while "very large" tropical cyclones have a radius of greater than 8 degrees (480 nmi, 888 km). Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius of the central dense overcast.
A tropical cyclone's primary energy source is the release of the heat of condensation from water vapor condensing at high altitudes, with solar heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical heat engine supported by mechanics driven by physical forces such as the rotation and gravity of the Earth. In another way, tropical cyclones could be viewed as a special type of mesoscale convective complex, which continues to develop over a vast source of relative warmth and moisture. Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy; the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives updrafts that increase the height of the storm clouds, speeding up condensation. This provides the system with enough energy to be self-sufficient and causes a positive feedback loop that continues as long as the tropical cyclone can draw energy from its thermal reservoir, the warm water at the surface of the ocean. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the Coriolis effect, giving it a cyclonic characteristic and affecting the trajectory of the storm.
What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection as a driving force. Because convection is strongest in a tropical climate, it defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclones draw their energy mostly from pre-existing horizontal temperature gradients in the atmosphere. To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to maintain the positive feedback loop running. As a result, when a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.
Scientists at the US National Center for Atmospheric Research estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules per day. That is about 1 PW (1015 watt). For comparison, this rate of energy release is equivalent to 70 times the world energy consumption of humans (and 200 times the world-wide electrical generating capacity), or to exploding a 10-megaton nuclear bomb every 20 minutes.
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. These high cirrus clouds may be the first signs of an approaching tropical cyclone when seen from dry land.
Major basins and related warning centers
On March 26, 2004, Cyclone Catarina became the first recorded South Atlantic cyclone and subsequently struck southern Brazil with winds equivalent to Category 2 on the Saffir-Simpson Hurricane Scale. As the cyclone formed outside of the authority of another warning center, Brazilian meteorologists initially treated the system as an extratropical cyclone, though subsequently classified it as tropical.
TimesWorldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active.
In the Northern Atlantic Ocean, a distinct hurricane season occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the Atlantic hurricane season is September 10. The Northeast Pacific Ocean has a broader period of activity, but in a similar time frame 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.
|Season lengths and seasonal averages|
|Basin||Season start||Season end||Tropical Storms
|Category 3+ TCs|
|Australia Southwest Pacific||October||May||10.6||4.8||1.9|
The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood. While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, water temperatures of at least 26.5 °C (80 °F) are needed down to a depth of at least 50 m (150 feet); waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms. Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone. High humidity is needed, especially in the lower-to-mid troposphere; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop. Low amounts of wind shear are needed, as high shear is disruptive to the storm's circulation. Tropical cyclones generally need to form more than 500 km (310 miles) or 5 degrees of latitude away from the equator, allowing the Coriolis effect to deflect winds blowing towards the low pressure center and creating a circulation. Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place.
LocationsMost tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Discontinuity (ITD), the Intertropical Convergence Zone (ITCZ), or the monsoon trough. Another important source of atmospheric instability is found in tropical waves, which cause about 85% of intense tropical cyclones in the Atlantic ocean, and become most of the tropical cyclones in the Eastern Pacific basin.
Tropical cyclones originate on the eastern side of oceans, but move west, intensifying as they move. Most of these systems form between 10 and 30 degrees away of the equator, and 87% form no farther away than 20 degrees of latitude, north or south. Because the Coriolis effect initiates and maintains tropical cyclone rotation, tropical cyclones rarely form or move within about 5 degrees of the equator, where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary as Tropical Storm Vamei did in 2001 and Cyclone Agni in 2004.
Movement and track
Steering windsAlthough tropical cyclones are large systems generating enormous energy, their movements over the Earth's surface are controlled by large-scale winds—the streams in the Earth's atmosphere. The path of motion is referred to as a tropical cyclone's track and has been analogized by Dr. Neil Frank, former director of the National Hurricane Center, to "leaves carried along by a stream."
Tropical systems, while generally located equatorward of the 20th parallel, are steered primarily westward by the east-to-west winds on the equatorward side of the subtropical ridge—a persistent high pressure area over the world's oceans. In the tropical North Atlantic and Northeast Pacific oceans, trade winds—another name for the westward-moving wind currents—steer tropical waves westward from the African coast and towards the Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen out. These waves are the precursors to many tropical cyclones within this region. In the Indian Ocean and Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the seasonal movement of the Intertropical Convergence Zone and the monsoon trough, rather than by easterly waves.
Coriolis effectCoriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents. The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward. The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the Northern Hemisphere usually turn north (before being blown east), and tropical cyclones in the Southern Hemisphere usually turn south (before being blown east) when no other effects counteract the Coriolis effect.
The Coriolis effect also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds - that force is the heat of condensation.
Interaction with the mid-latitude westerliessubtropical ridge axis, its general track around the high-pressure area is deflected significantly by winds moving towards the general low-pressure area to its north. When the cyclone track becomes strongly poleward with an easterly component, the cyclone has begun recurvature. A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of Japan to the north, and then to the northeast, if the typhoon encounters winds blowing northeastward toward a low-pressure system passing over China or Siberia. Many tropical cyclones are eventually forced toward the northeast by extratropical cyclones, which move from west to east to the north of the subtropical ridge. An example of a tropical cyclone in recurvature was Typhoon Ioke in 2006, which took a similar trajectory.
- See also: and
Interactions between typhoonsWhen two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after Dr. Sakuhei Fujiwhara.
Factorsextratropical cyclones. While there is a chance a tropical cyclone could regenerate if it managed to get back over open warm water, if it remains over mountains for even a short time, it can rapidly lose its structure. Many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall, leading to deadly floods and mudslides, similar to those that happened with Hurricane Mitch in 1998. Additionally, dissipation can occur if a storm remains in the same area of ocean for too long, mixing the upper 30 meters (100 feet) of water. This occurs because the cyclone draws up colder water from deeper in the sea through upwelling, and causes the water surface to become too cool to support the storm. Without warm surface water, the storm cannot survive.
A tropical cyclone can dissipate when it moves over waters significantly below 26.5 °C. This will cause the storm to lose its tropical characteristics (i.e. thunderstorms near the center and warm core) and become a remnant low pressure area, which can persist for several days. This is the main dissipation mechanism in the Northeast Pacific ocean. Weakening or dissipation can occur if it experiences vertical wind shear, causing the convection and heat engine to move away from the center; this normally ceases development of a tropical cyclone. Additionally, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days. 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. In the Pacific ocean and Atlantic ocean, such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane-force wind speeds when they reach the west coast of North America. These phenomena can also affect Europe, where they are known as European windstorms; Hurricane Iris's extratropical remnants became one in 1995. Additionally, a cyclone can merge with another area of low pressure, becoming a larger area of low pressure. This can strengthen the resultant system, although it may no longer be a tropical cyclone.
Artificial dissipationIn the 1960s and 1970s, the United States government attempted to weaken hurricanes through 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—a hurricane seeded in Project Stormfury—dropped as much as 30%, but Debby regained its strength after each of two seeding forays. In an earlier episode in 1947, disaster struck when a hurricane east of Jacksonville, Florida promptly changed its course after being seeded, and smashed into Savannah, Georgia. 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% chance of making landfall within 48 hours, greatly reducing the number of possible test storms. 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.
Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing icebergs into the tropical oceans. Other ideas range from covering the ocean in a substance that inhibits evaporation, dropping large quantities of ice into the eye at very early stages of development (so that the latent heat is absorbed by the ice, instead of being converted to kinetic energy that would feed the positive feedback loop), or blasting the cyclone apart with nuclear weapons. Project Cirrus even involved throwing dry ice on a cyclone. These approaches all suffer from one flaw above many others: tropical cyclones are simply too large for any of them to be practical.
Within the last two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million persons worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in shelters increase the risk of disease propagation. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and hamper reconstruction efforts.
Although cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes and polar regions. The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.
Observation and forecasting
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.
In-situ measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government hurricane hunters. 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. A similar mission was also completed successfully in the western Pacific ocean. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare.
- See also: Tropical cyclone forecasting
a best practice, as it allows them to determine a more accurate trajectory. High-speed computers and sophisticated simulation software allow forecasters to produce computer models that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. However, 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.
Classifications, terminology, and naming
Additionally, as indicated in the table below, each basin uses a separate system of terminology, making comparisons between different basins difficult. In the Pacific Ocean, hurricanes from the Central North Pacific sometimes cross the International Date Line into the Northwest Pacific, becoming typhoons (such as Hurricane/Typhoon Ioke in 2006); on rare occasions, the reverse will occur. It should also be noted that typhoons with sustained winds greater than 130 knots (240 km/h or 150 mph) are called Super Typhoons by the Joint Typhoon Warning Center.
A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained winds of less than 17 m/s (33 kt, 38 mph, or 62 km/h). It has no eye and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression." The practice of the Philippines is to name tropical depressions from their own naming convention when the depressions are within the Philippines' area of responsibility.
A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 and 32 m/s (34–63 kt, 39–73 mph, or 62–117 km/h). At this point, the distinctive cyclonic shape starts to develop, although an eye is not usually present. Government weather services, other than the Philippines, first assign names to systems that reach this intensity (thus the term named storm).
A hurricane or typhoon (sometimes simply referred to as a tropical cyclone, as opposed to a depression or storm) is a system with sustained winds of at least 33 m/s (64 kt, 74 mph, or 118 km/h). A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of 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 16–80 km (10–50 mi) wide in which the strongest thunderstorms and winds circulate around the storm's center. Maximum sustained winds in the strongest tropical cyclones have been estimated at about 85 m/s (165 kt, 190 mph, 305 km/h).
|Tropical Cyclone Classifications (all winds are 10-minute averages)|
|Beaufort scale||10-minute sustained winds (knots)||N Indian Ocean
|SW Indian Ocean
|NE Pacific &|
NHC & CPHC
|0–6||<28||Depression||Trop. Disturbance||Tropical Low||Tropical Depression||Tropical Depression||Tropical Depression||Tropical Depression|
|30–33||Tropical Storm||Tropical Storm|
|8–9||34–47||Cyclonic Storm||Moderate Tropical Storm||Trop. Cyclone (1)||Tropical Cyclone||Tropical Storm|
|10||48–55||Severe Cyclonic Storm||Severe Tropical Storm||Tropical Cyclone (2)||Severe Tropical Storm|
|12||64–72||Very Severe Cyclonic Storm||Tropical Cyclone||Severe Tropical Cyclone (3)||Typhoon|
|86–89||Severe Tropical Cyclone (4)||Major Hurricane (3)|
|90–99||Intense Tropical Cyclone|
|100–106||Major Hurricane (4)|
|107–114||Severe Tropical Cyclone (5)|
|115–119||Very Intense Tropical Cyclone||Super Typhoon|
|>120||Super Cyclonic Storm||Major Hurricane (5)|
Origin of storm termsChinese 大風 (Cantonese: daaih fūng; Mandarin: dà fēng) which means "great wind." (The Chinese term as 颱風 or 台风 táifēng, and 台風 taifū 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). Alternatively, the word may be derived from Urdu, Persian and Arabic ţūfān (طوفان), which in turn originates from Greek tuphōn (Τυφών), a monster in Greek mythology responsible for hot winds. The related Portuguese word tufão, used in Portuguese for any tropical cyclone, is also derived from Greek tuphōn.
The word hurricane, used in the North Atlantic and Northeast Pacific, is derived from the name of a native Caribbean Amerindian storm god, Huracan, via Spanish huracán. (Huracan is also the source of the word Orcan, another word for the European windstorm. These events should not be confused.) Huracan became the Spanish term for hurricanes probably because of this.
Notable tropical cyclones
The 1970 Bhola cyclone is the deadliest tropical cyclone on record, killing over 300,000 people and potentially as many as 1 million after striking the densely populated Ganges Delta region of Bangladesh on November 13, 1970. Its powerful storm surge was responsible for the high death toll. The North Indian cyclone basin has historically been the deadliest basin, with several cyclones since 1900 killing over 100,000 people, all in Bangladesh. Elsewhere, Typhoon Nina killed 29,000 in China due to a 2000-year flood which caused 62 dams including the Banqiao Dam to fail; another 145,000 died during the subsequent famine and epidemic. The Great Hurricane of 1780 is the deadliest Atlantic hurricane on record, killing about 22,000 people in the Lesser Antilles. A tropical cyclone does need not be particularly strong to cause memorable damage, primarily if the deaths are from rainfall or mudslides. Tropical Storm Thelma in November 1991 killed thousands in the Philippines, while in 1982, the unnamed tropical depression that eventually became Hurricane Paul killed around 1,000 people in Central America.
Hurricane Katrina is estimated as the costliest tropical cyclone worldwide, causing $81.2 billion in property damage (2005 USD) with overall damage estimates exceeding $100 billion (2005 USD). Katrina killed at least 1,836 people after striking Louisiana and Mississippi as a major hurricane in August 2005. The Galveston Hurricane of 1900 is the deadliest natural disaster in the United States, killing an estimated 6,000 to 12,000 people in Galveston, Texas. Hurricane Iniki in 1992 was the most powerful storm to strike Hawaii in recorded history, hitting Kauai as a Category 4 hurricane, killing six people, and causing U.S. $3 billion in damage. Other destructive Eastern Pacific hurricanes include Pauline and Kenna, both causing severe damage after striking Mexico as major hurricanes. In March 2004, Cyclone Gafilo struck northeastern Madagascar as a powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation for over 20 years.
Typhoon Tip in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 mbar (25.69 inHg) and maximum sustained wind speeds of 165 knots (190 mph, 305 km/h). Tip, however, does not solely hold the record for fastest sustained winds in a cyclone. Typhoon Keith in the Pacific and Hurricanes Camille and Allen in the North Atlantic currently share this record with Tip. Camille was the only storm to actually strike land while at that intensity, making it, with 165 knots (190 mph, 305 km/h) sustained winds and 210 mph (335 km/h) gusts, the strongest tropical cyclone on record at landfall. Typhoon Nancy in 1961 had recorded wind speeds of 185 knots (215 mph, 345 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 storm with the highest wind speeds on record. Similarly, a surface-level gust caused by Typhoon Paka on Guam was recorded at 205 knots (235 mph, 380 km/h). Had it been confirmed, it would be the strongest non-tornadic wind ever recorded on the Earth's surface, but the reading had to be discarded since the anemometer was damaged by the storm.
In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with tropical storm-force winds 2,170 km (1,350 miles) in diameter. The smallest storm on record, Cyclone Tracy, was roughly 100 km (60 miles) wide before striking Darwin, Australia in 1974.
Hurricane John is the longest-lasting tropical cyclone on record, lasting 31 days in 1994. Prior to the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations. John is the second longest-tracked tropical cyclone in the Northern Hemisphere on record, behind Typhoon Ophelia of 1960 which had a path of 8,500 miles (12,500 km). Reliable data for Southern Hemisphere cyclones is unavailable.
Long term activity trends
- See also: Atlantic hurricane reanalysis
Atlantic storms are becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. This can be attributed to the increased intensity and duration of hurricanes striking North America, and to a greater degree, the number of people living in susceptible coastal areas, following increased 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 may have gone unmeasured in some instances. 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, also known as the Atlantic Multidecadal Oscillation. 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, a record only recently exceeded in 2005, which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900-1925; however, many intense storms formed during 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. Some historical weather experts say these storms may have been as high as Category 4 in strength.
These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a ship reported a voyage through the storm or a storm hit land in a populated area. The official record, therefore, could miss 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.
- See also: Global warming
In an article in Nature, Kerry Emanuel stated that potential hurricane destructiveness, a measure combining hurricane strength, duration, and frequency, "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." Emanuel predicted "a substantial increase in hurricane-related losses in the twenty-first century.". Similarly, P.J. Webster and others published an article in Science examining the "changes in tropical cyclone number, duration, and intensity" over the last 35 years, the period when satellite data has been available. Their main finding was although the number of cyclones decreased throughout the planet excluding the north Atlantic Ocean, there was a great increase in the number and proportion of very strong cyclones.
The strength of the reported effect is surprising in light of modeling studies that predict only a one half category increase in storm intensity as a result of a ~2 °C global warming. Such a response would have predicted only a ~10% increase in Emanuel's potential destructiveness index during the twentieth century rather than the ~75-120% increase he reported. Secondly, after adjusting for changes in population and inflation, and despite a more than 100% increase in Emanuel's potential destructiveness index, no statistically significant increase in the monetary damages resulting from Atlantic hurricanes has been found.
Both Emanuel and Webster et al. consider sea surface temperatures to be vital in the development of cyclones. Though neither study can directly link hurricanes with global warming, the increase in sea surface temperatures is believed to be due to both global warming and nature variability, e.g. the hypothesized Atlantic Multidecadal Oscillation (AMO), though an exact attribution has not been defined. However, recent temperatures are the warmest ever observed for many ocean basins.
In February 2007, the United Nations Intergovernmental Panel on Climate Change released its fourth assessment report on climate change. The report noted many observed changes in the climate, including atmospheric composition, global average temperatures, ocean conditions, among others. The report concluded the observed increase in tropically intensity is larger than climate models predict. Additionally, the report considered that it is likely that storm intensity will continue to increase through the 21st century, and declared it more likely than not that there has been some human contribution to the increases in tropical cyclone intensity. However, there is no universal agreement about the magnitude of the effects anthropogenic global warming has on tropical cyclone formation, track, and intensity. For example, critics such as Chris Landsea assert that man-made effects would be "quite tiny compared to the observed large natural hurricane variability." A statement by the American Meteorological Society on February 1, 2007 stated that trends in tropical cyclone records offer "evidence both for and against the existence of a detectable anthropogenic signal" in tropical cyclogenesis. Albeit many aspects of a link between tropical cyclones and global warming are still being "hotly debated", a point of agreement is that no individual tropical cyclone or season can be attributed to global warming.
Related cyclone types
- See also: 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; additionally, although not as frequently, 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 when their low-pressure centers cause powerful winds and very high seas.
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 latitudes, from the equator to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm. From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.
Tropical cyclones in popular culture
- Annual seasons
Cyclones and Anticyclones of the world
- Forecasting and preparation
Extratropical - Meso-scale - Polar - Polar low - Subtropical - Tropical
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- Learning resources
- Surviving a hurricane - A guide for children and youth
- WMO guide on cyclone terminology
- Summary of cyclone terminology from NOAA FAQ
- NOVA scienceNOW: Hurricanes
This is not an image, but rather a PDF file.
- World Meteorological Organization Severe Weather Information Center - Shows all current tropical systems worldwide and their tracks
- Tropical Storms Worldwide - by Hawaii University
- FEMA for Kids: Hurricanes
- Regional specialised meteorological centers
- US National Hurricane Center - North Atlantic, Eastern Pacific
- Central Pacific Hurricane Center - Central Pacific
- Japan Meteorological Agency - NW Pacific
- India Meteorological Department - Bay of Bengal and the Arabian Sea
- Météo-France - La Reunion - South Indian Ocean from Africa to 90° E
- Fiji Meteorological Service - South Pacific east of 160°, north of 25° S
- Past storms
Tropical cyclogenesis is the technical term describing the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis
- Global climatology of tropical cyclones
- Unisys historical and contemporary hurricane track data
- United States Tropical Cyclone Rainfall Climatology - Nearly 30 years of tropical cyclone histories with an emphasis on storm total rainfall, in color, up to present. Broken up by year, region, by point of landfall, and North American countries impacted
- Global ISCCP B1 Browse System Satellite Archive
- Digital Typhoon: Typhoon Images and Information
..... Click the link for more information.eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km (20–40 miles) in diameter.
..... Click the link for more information.Presently, most tropical cyclones are given a name using one of several lists of tropical cyclone names. Storms of tropical storm strength are given names to allow the public to easily distinguish between systems when there are multiple systems in an individual basin at the
..... Click the link for more information.lists from which these tropical and subtropical cyclone names are derived.
North AtlanticNorth Atlantic Ocean storms are named by the U.S. National Hurricane Center from the following lists. There have been six lists of names in use since 1979 (List I).
..... Click the link for more information.This is a list of named tropical cyclones, giving all official names for tropical cyclones. This includes Atlantic hurricane and Northeastern Pacific hurricane names from 1950 to 2007, Northwestern Pacific Typhoon names from 1945 to 2007, and North Indian cyclone names from 2004 to
..... Click the link for more information.The effects of tropical cyclones are the impacts that tropical cyclones have on the areas they move to. The main destructive impacts include heavy rain, strong wind, large storm surges at landfall, and tornadoes. After the cyclone has passed, devastation continues.
..... Click the link for more information.See Severe weather terminology for a comprehensive article on this term and related weather terms.
..... Click the link for more information.A storm surge is an offshore rise of water associated with a low pressure weather system, typically a tropical cyclone. Storm surge is caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea level.
..... Click the link for more information.This is a list of notable tropical cyclones, subdivided by basin and reason for notability.
North Atlantic basin
- Main article: List of notable Atlantic hurricanes
- Main article: List of retired Atlantic hurricanes
..... Click the link for more information.Tropical cyclone names may be retired (removed from the name list) in several tropical cyclone basins around the world by the World Meteorological Organization. Usually, this is due to the tropical cyclone so named being a major human disaster.
..... Click the link for more information.This is a list of retired Atlantic hurricane names. Hurricane names are retired by the World Meteorological Organization (WMO) in a meeting in March or April of each year. Those hurricanes that have their names retired tend to be exceptionally destructive storms that often become
..... Click the link for more information.list of all Pacific hurricanes that have had their names retired. Hurricane names are retired by the World Meteorological Organization (WMO) in a meeting in March or April of each year.
..... Click the link for more information.Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the Pacific Ocean (considered separately because tropical cyclones rarely form in the central Pacific), the
..... Click the link for more information.A Regional Specialized Meteorological Centre (also Regional Specialized Meteorological Center and Regional Specialised Meteorological Centre) is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a
..... Click the link for more information.A Tropical Cyclone Warning Centre is one of six regional warning centers that are part of the World Meteorological Organization tropical cyclone programme, and act to observe, name, and forecast tropical cyclones in their respective sections of the world, supplementing the work of
..... Click the link for more information.Tropical Cyclone Classifications (all winds are 10-minute averages)
Beaufort scale 10-minute sustained winds (knots) N Indian Ocean
IMD SW Indian Ocean
BOM SW Pacific
FMS NW Pacific
JMA NW Pacific
JTWC NE Pacific &
NHC & CPHC
..... Click the link for more information.Tropical cyclone observation has been carried out over the past couple of centuries in various ways. The passage of typhoons, hurricanes, as well as other tropical cyclones have been detected by word of mouth from sailors recently coming to port or by radio transmissions from ships
..... Click the link for more information.Tropical cyclone rainfall forecasting involves using scientific models and other tools to predict the precipitation expected in tropical cyclones such as hurricanes and typhoons.
..... Click the link for more information.A tropical cyclone rainfall climatology is developed to determine rainfall characteristics of past tropical cyclones. A tropical cyclone rainfall climatology can be used to help forecast current or upcoming tropical cyclone impacts.
..... Click the link for more information.Nature, in the broadest sense, is equivalent to the natural world, physical universe, material world or material universe. "Nature" refers to the phenomena of the physical world, and also to life in general.
..... Click the link for more information.weather is the set of all extant phenomena in a given atmosphere at a given time. The term usually refers to the activity of these phenomena over short periods (hours or days), as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of
..... Click the link for more information.hurricane is commonly used to designate a severe form of tropical cyclone but may also refer to:
- In general international terminology, a Hurricane is any wind of the strongest level on the Beaufort scale.
..... Click the link for more information.Typhoon can refer to:
- Tropical cyclones in the Northern Pacific Ocean
- Pacific typhoon
- Typhon, a monster in Greek mythology
- Typhoon, a class of Soviet submarines
- Typhoon Naval Stabilized Weapon System
- the Eurofighter Typhoon, a multirole combat aircraft.
..... Click the link for more information.storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather. It may be marked by strong wind, thunder and lightning (a thunderstorm), heavy precipitation, such as ice (ice storm), or wind transporting
..... Click the link for more information.low for short, is a region where the atmospheric pressure is lowest with relation to the surrounding area. Tropical storms, extratropical cyclones, subpolar cyclones, and subarctic cyclones are called low-pressure cells in some English-speaking communities.
..... Click the link for more information.thunderstorm, also called an electrical storm or lightning storm, is a form of weather characterized by the presence of lightning and its attendant thunder produced from a cumulonimbus cloud.
..... Click the link for more information.Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. Condensation commonly occurs when a vapor is cooled to a liquid, but can also occur if a vapor is compressed (i.e.
..... Click the link for more information.nor'easter (also northeaster; see below) is a macro-scale storm whose winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada.
..... Click the link for more information.European windstorm is a severe cyclonic storm that tracks across the North Atlantic towards northwestern Europe in the winter months. These storms usually track over the north coast of Scotland towards Norway but can veer south to affect other countries including England, Wales,
..... Click the link for more information.polar low is a small-scale, short-lived atmospheric low pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres.
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