A tropical cyclone is a rapidly rotating storm system
characterized by a low-pressure
center, a closed low-level atmospheric circulation
, strong winds
, and a spiral arrangement of thunderstorm
s that produce heavy rain and/or squall
s. Depending on its location and strength, a tropical cyclone is referred to by different names
, including hurricane (), typhoon (), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane
is a tropical cyclone that occurs in the Atlantic Ocean
and northeastern Pacific Ocean
, and a typhoon
occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean
, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".
"Tropical" refers to the geographical origin of these systems, which form almost exclusively over tropical
seas. "Cyclone" refers to their winds moving in a circle, whirling round their central clear eye
, with their winds blowing counterclockwise
in the Northern Hemisphere
in the Southern Hemisphere
. The opposite direction of circulation is due to the Coriolis effect
. Tropical cyclones typically form
over large bodies of relatively warm water. They derive their energy through the evaporation of water
from the ocean
surface, which ultimately recondenses
s and rain when moist air rises and cools to saturation
. This energy source
differs from that of mid-latitude cyclonic storms
, such as nor'easter
s and European windstorm
s, which are fueled primarily by horizontal temperature contrasts
. Tropical cyclones are typically between 100 and 2,000 km (60 and 1,240 mi) in diameter. Every year tropical cyclones impact various regions of the globe including the Gulf Coast of North America, Australia, India and Bangladesh.
The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum
imparted by the Earth's rotation
as air flows inwards toward the axis of rotation. As a result, they rarely form within 5° of the equator. Tropical cyclones are almost unknown in the South Atlantic due to a consistently strong wind shear
and a weak Intertropical Convergence Zone
. Conversely, the African easterly jet
and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea
, while cyclones near Australia owe their genesis to the Asian monsoon
and Western Pacific Warm Pool
The primary energy source for these storms is warm ocean waters. These storms are therefore typically strongest when over or near water, and weaken quite rapidly over land. This causes coastal regions to be particularly vulnerable to tropical cyclones, compared to inland regions. Coastal damage may be caused by strong winds and rain, high waves (due to winds), storm surge
s (due to wind and severe pressure changes), and the potential
of spawning tornado
es. Tropical cyclones draw in air from a large area and concentrate the water content of that air (from atmospheric moisture and moisture evaporated from water) into precipitation
over a much smaller area. This replenishing of moisture-bearing air after rain may cause multi-hour or multi-day extremely heavy rain up to from the coastline, far beyond the amount of water that the local atmosphere holds at any one time. This in turn can lead to river flooding
, overland flooding, and a general overwhelming of local water control structures across a large area. Although their effects on human populations can be devastating, tropical cyclones may play a role in relieving drought conditions, though this claim is disputed. They also carry heat and energy away from the tropics and transport it towards temperate latitudes, which plays an important role in regulating global climate.
A tropical cyclone is the generic term for a warm-cored, non-frontal synoptic-scale low-pressure system
waters around the world.
The systems generally have a well-defined center which is surrounded by deep atmospheric convection
and a closed wind circulation at the surface.
Historically tropical cyclones have occurred around the world for thousands of years, with one of the earliest tropical cyclones on record estimated to have occurred in Western Australia in around 6000 BC.
However, before satellite imagery became available during the 20th century, many of these systems went undetected unless it impacted land or a ship encountered it by chance.
These days, on average around 80 to 90 named tropical cyclones form each year around the world, of which over half of which develop hurricane-force winds of or more.
Around the world, a tropical cyclone is generally deemed to have formed, once mean surface winds in excess of are observed.
It is assumed at this stage that a tropical cyclone has become self-sustaining and can continue to intensify without any help from its environment.
Tropical cyclones on either side of the Equator generally have their origins in the Intertropical Convergence Zone
, where winds blow from either the northeast or southeast.
Within this broad area of low-pressure air is heated over the warm tropical ocean and rises in discrete parcels which causes thundery showers to form.
These showers dissipate quite quickly, however, they can group together into large clusters of thunderstorms.
This creates a flow of warm, moist, rapidly rising air, which starts to rotate cyclonically
as it interacts with the rotation of the earth.
There are several factors required for these thunderstorms to develop further, including sea surface temperatures of around and low vertical windshear surrounding the system.
Eye and center
At the center of a mature tropical cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear "eye
". Weather in the eye is normally calm and free of convective clouds, although the sea may be extremely violent.
The eye is normally circular and is typically in diameter, though eyes as small as and as large as have been observed.
The cloudy outer edge of the eye is called the "eyewall". The eyewall typically expands outward with height, resembling an arena football stadium; this phenomenon is sometimes referred to as the "stadium effect
The eyewall is where the greatest wind speeds are found, air rises most rapidly, clouds reach their highest altitude
, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land.
In a weaker storm, the eye may be obscured by the central dense overcast
, which is the upper-level cirrus shield that is associated with a concentrated area of strong thunderstorm activity near the center of a tropical cyclone.
The eyewall may vary over time in the form of eyewall replacement cycles
, particularly in intense tropical cyclones. Outer rainbands
can organize into an outer ring of thunderstorms that slowly moves inward, which is believed to rob the primary eyewall of moisture and angular momentum
. When the primary eyewall weakens, the tropical cyclone weakens temporarily. The outer eyewall eventually replaces the primary one at the end of the cycle, at which time the storm may return to its original intensity.
Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperature
s 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 month. November is the only month in which all the tropical cyclone basins
are in season.
In the Northern Atlantic Ocean
, a distinct cyclone 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 March 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, the tropical cyclone year begins on July 1 and runs all year-round encompassing the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.
Interaction with the upper ocean
The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean with the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature
over a large area in just a few days.
Conversely, the mixing of the sea can result in heat being inserted in deeper waters, with potential effects
on global climate
The movement of a tropical cyclone (i.e. its "track") is typically approximated as the sum of two terms: "steering" by the background environmental wind and "beta drift".
Environmental steering is the primary influence on the motion of tropical cyclones.
Conceptually, it represents the movement of the storm due to prevailing winds and other wider environmental conditions, similar to "leaves carried along by a stream".
Physically, the winds, or flow field
, in the vicinity of a tropical cyclone may be treated as having two parts: the flow associated with the storm itself, and the large-scale background flow of the environment in which the storm takes place.
Tropical cyclones can be treated as local maxima of vorticity
suspended within the large-scale background flow of the environment in which the storm takes place.
In this way, tropical cyclone motion may be represented to first-order simply as advection
of the storm by the local environmental flow.
This environmental flow is termed the "steering flow" and is the dominant influence on tropical cyclone motion.
The strength and direction of the steering flow can be approximated as an vertical integration of the winds blowing horizontally in the cyclone's vicinity weighted by the altitude at which those winds are occurring. Because winds can vary with height, determining the steering flow precisely can be difficult. The pressure altitude
at which the background winds are most correlated with a tropical cyclone's motion is known as the "steering level".
The motion of stronger tropical cyclones is more correlated with the background flow averaged across a thicker portion of troposphere
compared to weaker tropical cyclones whose motion is more correlated with the background flow averaged across a narrower extent of the lower troposphere.
When wind shear and latent heat
release is present, tropical cyclones tend to move towards regions where potential vorticity
is increasing most quickly with respect to time.
Climatologically, tropical cyclones are steered primarily westward by the east-to-west trade winds
on the equatorial side of the subtropical ridge
—a persistent high-pressure area over the world's subtropical oceans.
In the tropical North Atlantic and Northeast Pacific oceans, the trade winds steer tropical easterly waves
westward from the African coast toward 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 contrast, in the Indian Ocean
and Western Pacific in both hemispheres, tropical cyclogenesis is influenced less by tropical easterly waves and more by the seasonal movement of the Inter-tropical Convergence Zone and the monsoon trough.
Other weather systems such as mid-latitude trough
s and broad monsoon gyres can also influence tropical cyclone motion by modifying the steering flow.
In addition to environmental steering, a tropical cyclone will tend to drift poleward and westward, a motion known as "beta drift".
This motion is due to the superposition of a vortex, such as a tropical cyclone, onto an environment in which the Coriolis force
varies with latitude, such as on a sphere or beta plane
The magnitude of the component of tropical cyclone motion associated with the beta drift ranges between 1–3 m/s (4–11 km/h, 2–7 mph) and tends to be larger for more intense tropical cyclones and at higher latitudes. It is induced indirectly by the storm itself as a result of a feedback between the cyclonic flow of the storm and its environment.
Physically, the cyclonic circulation of the storm advects environmental air poleward east of center and equatorial west of center. Because air must conserve its angular momentum
, this flow configuration induces a cyclonic gyre equatorward and westward of the storm center and an anticyclonic gyre poleward and eastward of the storm center. The combined flow of these gyres acts to advect the storm slowly poleward and westward. This effect occurs even if there is zero environmental flow.
Due to a direct dependence of the beta drift on angular momentum, the size of a tropical cyclone can impact the influence of beta drift on its motion; beta drift imparts a greater influence on the movement of larger tropical cyclones than that of smaller ones.
Multiple storm interaction
A third component of motion that occurs relatively infrequently involves the interaction of multiple tropical cyclones. When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. Depending on their separation distance and strength, the two vortices may simply orbit around one another or else may 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 Sakuhei Fujiwhara
Interaction with the mid-latitude westerlies
Though a tropical cyclone typically moves from east to west in the tropics, its track may shift poleward and eastward either as it moves west of the subtropical ridge axis or else if it interacts with the mid-latitude flow, such as the jet stream
or an extratropical cyclone
. This motion, termed "recurvature", commonly occurs near the western edge of the major ocean basins, where the jet stream typically has a poleward component and extratropical cyclones are common. An example of tropical cyclone recurvature was Typhoon Ioke in 2006.
There are a variety of metrics commonly used to measure storm size. The most common metrics include the radius of maximum wind, the radius of 34-knot wind (i.e. gale force
), the radius of outermost closed isobar
), and the radius of vanishing wind.
An additional metric is the radius at which the cyclone's relative vorticity
field decreases to 1×10−5
On Earth, tropical cyclones span a large range of sizes, from as measured by the radius of vanishing wind. They are largest on average in the northwest Pacific Ocean basin and smallest in the northeastern Pacific Ocean
If the radius of outermost closed isobar is less than two degrees of latitude
(), then the cyclone is "very small" or a "midget". A radius of 3–6 latitude degrees () is considered "average sized". "Very large" tropical cyclones have a radius of greater than 8 degrees ().
Observations indicate that size is only weakly correlated to variables such as storm intensity (i.e. maximum wind speed), radius of maximum wind, latitude, and maximum potential intensity.
On occasion, tropical cyclones may undergo a process known as rapid intensification, a period in which the maximum sustained winds of a tropical cyclone increase by 30 knots or more within 24 hours.
For rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely high (near or above 30 °C, 86 °F), and water of this temperature must be sufficiently deep such that waves do not upwell cooler waters to the surface. On the other hand, Tropical Cyclone Heat Potential
is one of such non-conventional subsurface oceanographic
parameters influencing the cyclone
intensity. Wind shear
must be low; when wind shear is high, the convection
and circulation in the cyclone will be disrupted. Usually, an anticyclone
in the upper layers of the troposphere
above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently.
However, some cyclones such as Hurricane Epsilon
have rapidly intensified despite relatively unfavorable conditions.
There are a number of ways a tropical cyclone can weaken, dissipate or lose its tropical characteristics, these include making landfall, moving over cooler water, encountering dry air or interacting with other weather systems. However, once a system has been declared dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable.
Should a tropical cyclone make landfall or pass over an island, then its circulation could start to break down, especially if it is a mountainous island.
Should a system make landfall on a large landmass, it would be cut off from its supply of warm moist maritime air and would start to draw in dry continental air.
This combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone.
Over a mountainous terrain, a system can quickly weaken, however, over flat areas, it may take two to three days for the circulation to break down and dissipate.
A tropical cyclone can dissipate when it moves over waters significantly cooler than . This will cause the storm to lose its tropical characteristics, such as a warm core with thunderstorms near the center, and become a remnant low-pressure area
. These remnant systems may persist for up to several days before losing their identity. This dissipation mechanism is most common in the eastern North Pacific. 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.
In addition, 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.
Over the years, there have been a number of techniques considered to try and artificially modify tropical cyclones.
These techniques have included using nuclear weapons, cooling the ocean with icebergs, blowing the storm away from land with giant fans and seeding
selected storms with dry ice or silver iodide
However, these techniques have failed to appreciate the duration, intensity, power or size of tropical cyclones.
Nomenclature and intensity classifications
Around the world, tropical cyclones are classified in different ways, based on the location, the structure of the system and its intensity. For example, within the Northern Atlantic and Eastern Pacific basins, a tropical cyclone with wind speeds of over is called a hurricane, while it is called a typhoon or a severe cyclonic storm within the Western Pacific or North Indian Oceans.
Within the Southern Hemisphere, it is either called a hurricane, tropical cyclone or a severe tropical cyclone, depending on if it is located within the South Atlantic, South-West Indian Ocean, Australian region or the South Pacific Ocean.
Tropical cyclones that develop around the world are assigned an identification code consisting of a two-digit number and suffix letter by the warning centers that monitor them. These codes start at 01 every year and are assigned in order to systems, which have the potential to develop further, cause significant impact to life and property or when the warning centers start to write advisories on the system.
The practice of using names to identify tropical cyclones goes back many years, with systems named after places or things they hit before the formal start of naming.
The system currently used provides positive identification of severe weather systems in a brief form, that is readily understood and recognized by the public.
The credit for the first usage of personal names for weather systems is generally given to the Queensland Government
Meteorologist Clement Wragge
who named systems between 1887 and 1907.
This system of naming weather systems subsequently fell into disuse for several years after Wragge retired, until it was revived in the latter part of World War II
for the Western Pacific.
Formal naming schemes have subsequently been introduced for the North and South Atlantic, Eastern, Central, Western and Southern Pacific basins as well as the Australian region and Indian Ocean.
At present, tropical cyclones are officially named by one of twelve meteorological services
and retain their names throughout their lifetimes to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings.
Since the systems can last a week or longer and more than one can be occurring in the same basin at the same time, the names are thought to reduce the confusion about what storm is being described.
Names are assigned in order from predetermined lists
with one, three, or ten-minute sustained wind speeds of more than depending on which basin it originates.
However, standards vary from basin to basin with some tropical depressions named in the Western Pacific, while tropical cyclones have to have a significant amount of gale-force winds occurring around the center before they are named within the Southern Hemisphere
The names of significant tropical cyclones in the North Atlantic Ocean, Pacific Ocean, and Australian region are retired from the naming lists and replaced with another name.
Major basins and related warning centers
The majority of tropical cyclones each year form in one of seven tropical cyclone basins, which are monitored by a variety of meteorological services and warning centres.
Ten of these warning centres worldwide are designated as either a Regional Specialized Meteorological Centre
or a Tropical Cyclone Warning Centre by the World Meteorological Organisation
's tropical cyclone programme.
These warning centres issue advisories which provide basic information and cover a systems present, forecast position, movement and intensity, in their designated areas of responsibility.
Meteorological services around the world are generally responsible for issuing warnings for their own country, however, there are exceptions, as the United States National Hurricane Center and Fiji Meteorological Service issue alerts, watches and warnings for various island nations in their areas of responsibility.
The United States Joint Typhoon Warning Center
(JTWC) and Fleet Weather Center (FWC) also publicly issue warnings, about tropical cyclones on behalf of the United States Government
The Brazilian Navy
Hydrographic Center names South Atlantic tropical cyclone
s, however the South Atlantic is not a major basin, and not an official basin according to the WMO.
Ahead of the formal season starting, people are urged to prepare for the effects of a tropical cyclone by politicians and weather forecasters amongst others. They prepare by determining their risk to the different types of weather, tropical cyclones cause, checking their insurance coverage and emergency supplies, as well as determining where to evacuate to if needed.
When a tropical cyclone develops and is forecast to impact land each member nation of the World Meteorological Organization
issues various watches and warnings
to cover the expected impacts.
However, there are some exceptions with the United States National Hurricane Center and Fiji Meteorological Service responsible for issuing or recommending warnings for other nations in their area of responsibility.
Tropical cyclones out at sea cause large waves, heavy rain
and high winds, disrupting international shipping and, at times, causing shipwrecks.
Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent tropical cyclones.
On land, strong wind
s can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The storm surge
, or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.
The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes
. Tornadoes can also be spawned as a result of eyewall mesovortices
, which persist until landfall.
Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million people 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 the hampering of reconstruction efforts.
On average, the Gulf and east coasts of the United States suffer approximately US$5 billion (1995 US $) in cyclone damage every year. The majority (83%) of tropical cyclone damage is caused by severe hurricanes, category 3 or greater. However, category 3 or greater hurricanes only account for about one-fifth of cyclones that make landfall every year.
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.
[National Oceanic and Atmospheric Administration]
2005 Tropical Eastern North Pacific Hurricane Outlook.
. Retrieved May 2, 2006.
Their precipitation may also alleviate drought conditions by restoring soil moisture, though one study focused on the Southeastern United States
suggested tropical cyclones did not offer significant drought recovery.
Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes
and polar regions,
and by regulating the thermohaline circulation
. 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.
When hurricanes surge upon shore from the ocean, salt is introduced to many freshwater areas and raises the salinity
levels too high for some habitats to withstand. Some are able to cope with the salt and recycle it back into the ocean, but others can not release the extra surface water quickly enough or do not have a large enough freshwater source to replace it. Because of this, some species of plants and vegetation die due to the excess salt. In addition, hurricanes can carry toxins
onshore when they make landfall. The flood water can pick up the toxins from different spills and contaminate the land that it passes over. These toxins are harmful to the people and animals in the area, as well as the environment around them. The flooding water can also spark oil spills.
Hurricane response is the disaster response
after a hurricane. Activities performed by hurricane responders include assessment, restoration, and demolition of buildings; removal of debris
and waste; repairs to land-based and maritime infrastructure
; and public health services including search and rescue
operations. Hurricane response requires coordination between federal, tribal, state, local, and private entities. According to the National Voluntary Organizations Active in Disaster
, potential response volunteers should affiliate with established organizations and should not self-deploy, so that proper training and support can be provided to mitigate the danger and stress of response work.
Hurricane responders face many hazards. Hurricane responders may be exposed to chemical and biological contaminants including stored chemicals, sewage
, human remains
, and mold
growth encouraged by flooding,
as well as asbestos
that may be present in older buildings.
Common injuries arise from falls
from heights, such as from a ladder or from level surfaces; from electrocution
in flooded areas, including from backfeed
from portable generators; or from motor vehicle accidents
Long and irregular shifts
may lead to sleep deprivation
, increasing the risk of injuries, and workers may experience mental stress associated with a traumatic incident
. Additionally, heat stress
is a concern as workers are often exposed to hot and humid temperatures, wear protective clothing and equipment, and have physically difficult tasks.
Tropical cyclones have occurred around the world for millennia. Sediment records in Western Australia suggest an intense tropical cyclone in the 4th millennium BC
Before satellite imagery became available during the 20th century, many of these systems went undetected unless it impacted land or a ship encountered it by chance.
However, reanalyses and research are being undertaken to extend the historical record, through the usage of poxy data
such as overwash deposits, beach ridges and historical documents such as diaries.
During the 1940s, routine aircraft reconnaissance started in both the Atlantic and Western Pacific basin during the mid-1940s, which provided ground truth data, however, early flights were only made once or twice a day.
Polar-orbiting weather satellites were first launched by the United States National Aeronautics and Space Administration
during 1960, but were not declared operational until 1965.
However, it took several years for some of the warning centres to take advantage of this new viewing platform and develop the expertise to associate satellite signatures with storm position and intensity.
Influence of climate
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.
Paleoclimate and natural variability
Major tropical cylones leave traces in overwash records
and shell layers in some coastal areas, which have been used to gain insight in hurricane activity over the past thousands of years.
Proxy records based on paleotempestological
research have revealed that major hurricane activity along the Gulf of Mexico coast varies on timescales of centuries to millennia.
Few major hurricanes struck the Gulf coast during 3000–1400 BC and again during the most recent millennium. These quiescent intervals were separated by a hyperactive period during 1400 BC and 1000 AD, when the Gulf coast was struck frequently by catastrophic hurricanes and their landfall probabilities increased by 3–5 times. This millennial-scale variability has been attributed to long-term shifts in the position of the Azores High
which may also be linked to changes in the strength of the North Atlantic oscillation
Of various modes of variability
in the climate system, El Niño-Southern Oscillation
has the largest impact on tropical cyclone activity.
Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies
. When the subtropical ridge
position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience much fewer September–November tropical cyclone impacts during El Niño
and neutral years.
During La Niña
years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat to China and much greater intensity in the Philippines
The Atlantic Ocean experiences depressed activity due to increased vertical wind shear
across the region during El Niño years. Tropical cyclones are further influenced by the Atlantic Meridional Mode
, the Quasi-biennial oscillation
and the Madden–Julian oscillation
Climate change can affect tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, a decrease in overall frequency, an increase in frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the possible consequences of human-induced climate change.
Tropical cyclones use warm, moist air as their fuel. As climate change is warming ocean temperatures
, there is potentially more of this fuel available. Between 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on the Saffir–Simpson scale
. The trend was most clear in the North Atlantic and in the Southern Indian Ocean. In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period. With 2 °C warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength.
A 2019 study indicates that climate change has been driving the observed trend of rapid intensification
of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities.
There is currently no consensus on how climate change will affect the overall frequency of tropical cyclones.
A majority of climate model
s show a decreased frequency in future projections.
For instance, a 2020 paper comparing nine high-resolution climate models found robust decreases in frequency in the Southern Indian Ocean and the Southern Hemisphere more generally, while finding mixed signals for Northern Hemisphere tropical cyclones. Observations have shown little change in the overall frequency of tropical cyclones worldwide, with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific.
There has been a poleward expansion of the latitude at which the maximum intensity of tropical cyclones occurs, which may be associated with climate change. In the North Pacific, there may also have been an eastward expansion.
Between 1949 and 2016, there was a slowdown in tropical cyclone translation speeds. It is unclear still to what extent this can be attributed to climate change: climate models do not all show this feature.
Warmer air can hold more water vapor: the theoretical maximum water vapor content is given by the Clausius–Clapeyron relation
, which yields ≈7% increase in water vapor in the atmosphere per 1 °C warming.
All models that were assessed in a 2019 review paper show a future increase of rainfall rates.
Additional sea level rise
will increase storm surge levels.
It is plausible that extreme wind wave
s see an increase as a consequence of changes in tropical cyclones, further exacerbating storm surge dangers to coastal communities.
The compounding effects from floods, storm surge, and terrestrial flooding (rivers) are projected to increase due to global warming
Observation and forecasting
Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and weather station
s, being relatively sparse, are rarely available on the site of the storm itself. In general, surface observations are available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Real-time measurements are usually taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.
Tropical cyclones are tracked by weather satellite
s capturing visible
images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based Doppler weather radar
. Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes.
Other satellites provide information from the perturbations of GPS
signals, providing thousands of snapshots per day and capturing atmospheric temperature, pressure, and moisture content.
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
These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch GPS dropsonde
s 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.
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 are not as skillful at predicting the intensity of tropical cyclones.
The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development. New tropical cyclone position and forecast information is available at least every six hours from the various warning centers.
Related cyclone types
In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as extratropical cyclone
s and subtropical cyclone
s, can be stages a tropical cyclone passes through during its formation
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; 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 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.
Notable tropical cyclones
Tropical cyclones that cause extreme destruction are rare, although when they occur, they can cause great amounts of damage or thousands of fatalities.
The 1970 Bhola cyclone
is considered to be the deadliest tropical cyclone on record, which killed around 300,000 people, 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.
Elsewhere, Typhoon Nina
killed nearly 100,000 in China in 1975 due to a 100-year flood
that caused 62 dams including the Banqiao Dam
to fail. The Great Hurricane of 1780
is the deadliest North Atlantic hurricane
on record, killing about 22,000 people in the Lesser Antilles
A tropical cyclone does not need to 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,
although the strongest typhoon to ever make landfall on record was Typhoon Haiyan
in November 2013, causing widespread devastation in Eastern Visayas
, and killing at least 6,300 people in the Philippines alone. In 1982, the unnamed tropical depression that eventually became Hurricane Paul
killed around 1,000 people in Central America
and Hurricane Katrina
are estimated to be the costliest tropical cyclones to impact the United States mainland, each causing damage estimated at $125 billion.
Harvey killed at least 90 people in August 2017 after making landfall
as a low-end Category 4 hurricane
. Hurricane Katrina is estimated as the second-costliest tropical cyclone worldwide,
causing $81.2 billion in property damage (2008 USD) alone,
with overall damage estimates exceeding $100 billion (2005 USD).
Katrina killed at least 1,836 people after striking Louisiana
as a major hurricane
in August 2005.
is the third most destructive tropical cyclone in U.S. history, with damage totaling $91.61 billion (2017 USD), and with damage costs at $68.7 billion (2012 USD), Hurricane Sandy
is the fourth most destructive tropical cyclone in U.S history. 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 Mitch
caused more than 10,000 fatalities in Central America, making it the second deadliest Atlantic hurricane in history. 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
, 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 more than 20 years.
The most intense storm on record is Typhoon Tip
in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of and maximum sustained wind speeds of or .
The highest maximum sustained wind speed ever recorded was or in Hurricane Patricia
in 2015—the most intense cyclone ever recorded in the Western Hemisphere. Typhoon Nancy
in 1961 also had recorded wind speeds of or , but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and thus it is no longer considered the storm with the highest wind speed on record.
Likewise, a surface-level gust caused by Typhoon Paka
on Guam in late 1997 was recorded at or . 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.
The World Meteorological Organization
established Barrow Island (Queensland)
as the location of the highest non-tornado related wind gust at
[World Record Wind Gust: 408 km/h](_blank)
. World Meteorological Organization.
on April 10, 1996, during Severe Tropical Cyclone Olivia
In addition to being the most intense tropical cyclone on record based on pressure, Tip is the largest cyclone on record, with tropical storm-force winds in diameter. The smallest storm on record, Tropical Storm Marco
, formed during October 2008 and made landfall in Veracruz
. Marco generated tropical storm-force winds only in diameter. Marco broke the record of 1974's Cyclone Tracy
is the longest-lasting tropical cyclone on record, lasting 31 days in 1994
. Before the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations.
John is also the longest-tracked tropical cyclone in the Northern Hemisphere on record, with a path of .
of the 1993–94 South Pacific
and Australian region
cyclone seasons had one of the longest tracks observed within the Southern Hemisphere, traveling a distance of over during December 1993 and January 1994.
In popular culture
, tropical cyclones have made several appearances in different types of media, including films, books, television, music, and electronic game
These media often portray tropical cyclones that are either entirely fiction
al or based on real events.
For example, George Rippey Stewart
'', a best-seller
published in 1941, is thought to have influenced meteorologists on their decision to assign female names to Pacific tropical cyclones.
Another example is the hurricane in ''The Perfect Storm
'', which describes the sinking of the ''Andrea Gail
'' by the 1991 Perfect Storm
Hurricanes have been featured in parts of the plots of series such as ''The Simpsons
'', ''Family Guy
'', ''Dawson's Creek
'', ''Burn Notice
'' and ''CSI: Miami
The 2004 film ''The Day After Tomorrow
'' includes several mentions of actual tropical cyclones and features fantastical "hurricane-like", albeit non-tropical, Arctic storms.
* Tropical meteorology
* Disaster preparedness
* Extraterrestrial vortex
* Space hurricane
* Hurricane Alley
* List of wettest tropical cyclones by country
* Outline of tropical cyclones
Forecasting and preparation
* Catastrophe modeling
* Tropical cyclone engineering
* Hurricane-proof building
Tropical cyclone seasons
* Tropical cyclones in
* Atlantic hurricane
( Atlantic hurricane season
* Pacific hurricane season
( Pacific hurricane season
* Pacific typhoon season
( Pacific typhoon season
* North Indian Ocean tropical cyclone
( North Indian Ocean cyclone season
* South-West Indian Ocean tropical cyclone
( South-West Indian Ocean cyclone season
* Australian region tropical cyclone
( Australian region cyclone season
* South Pacific tropical cyclone
( South Pacific cyclone season
* Mediterranean tropical-like cyclone
* South Atlantic tropical cyclone
United States National Hurricane Center
nbsp;– North Atlantic, Eastern Pacific
United States Central Pacific Hurricane Center
nbsp;– Central Pacific
Japan Meteorological Agency
nbsp;– Western Pacific
India Meteorological Department
nbsp;– Indian Ocean
Météo-France – La Reunion
nbsp;– South Indian Ocean from 30°E to 90°E
Indonesian Meteorological Department
nbsp;– South Indian Ocean from 90°E to 125°E, north of 10°S
Australian Bureau of Meteorology
nbsp;– South Indian Ocean and South Pacific Ocean from 90°E to 160°E
Papua New Guinea National Weather Service
nbsp;– South Pacific east of 160°E, north of 10°S
Fiji Meteorological Service
nbsp;– South Pacific west of 160°E, north of 25° S
MetService New Zealand
nbsp;– South Pacific west of 160°E, south of 25°S
Category:Articles containing video clips
Category:Climate change and hurricanes
Category:Types of cyclone