Tropical_cyclone

Size

One measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed isobar, also known as its ROCI. If the radius is less than two degrees of latitude or 222 kilometres (138 mi), then the cyclone is "very small" or a "midget". Radii between 3 and 6 latitude degrees or 333 kilometres (207 mi) to 666 kilometres (414 mi) are considered "average sized". "Very large" tropical cyclones have a radius of greater than 8 degrees or 888 kilometres (552 mi).Joint Typhoon Warning Center. Q: What is the average size of a tropical cyclone? Retrieved on 2007-07-04. Other methods of determining a tropical cyclone\'s size include measuring the radius of gale force winds and measuring the radius at which its relative vorticity field decreases to 1×10^-5 s^-1 from its center.Bureau of Meteorology. Global Guide to Tropical Cyclone Forecasting: CHAPTER 2: TROPICAL CYCLONE STRUCTURE 2.4 OUTER STRUCTURE. Retrieved on 2008-02-24.K. S. Liu and Johnny C. L. Chan (December 1999). "Size of Tropical Cyclones as Inferred from ERS-1 and ERS-2 Data". Monthly Weather Review 127 (12). Retrieved on 2008-02-24. 

Mechanics

Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a positive feedback loop over warm ocean waters.Kerry Emanuel. Anthropogenic Effects on Tropical Cyclone Activity. Retrieved on 2008-02-25.

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.National Weather Service (September 2006). Hurricanes... Unleashing Nature\'s Fury: A Preparedness Guide (PDF). NOAA. Retrieved on 2006-12-02. 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;Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why don\'t we try to destroy tropical cyclones by nuking them?. NOAA. Retrieved on 2006-07-25. 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.National Oceanic & Atmospheric Administration (August 2001). NOAA Question of the Month: How much energy does a hurricane release?. NOAA. Retrieved on 2006-03-31. This positive feedback loop continues for as long as conditions are favorable for tropical cyclone development. 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,Encyclopædia Britannica. Coriolis force (physics). Retrieved on 2008-02-25. giving it a cyclonic characteristic and affecting the trajectory of the storm.Encyclopædia Britannica. Tropical cyclone: Tropical cyclone tracks. Retrieved on 2008-02-25.

What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection as a driving force.Bureau of Meteorology. How are tropical cyclones different to mid-latitude cyclones?. Frequently Asked Questions. Retrieved on 2006-03-31. 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. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Doesn\'t the friction over land kill tropical cyclones?. NOAA. Retrieved on 2006-07-25.

Chart displaying the drop in surface temperature in the Gulf of Mexico as Hurricanes Katrina and Rita passed over

The passage of a tropical cyclone over the ocean can cause the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. Cooling is primarily caused by upwelling of cold water from deeper in the ocean due to the wind stresses the storm itself induces upon the sea surface. Additional cooling may come in the form of cold water from falling raindrops. 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.Eric A. D\'Asaro and Peter G. Black. (2006). J8.4 Turbulence in the Ocean Boundary Layer Below Hurricane Dennis. University of Washington. Retrieved on 2008-02-22.

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 (10¹⁸ J) per day, equivalent to about 1 PW (10¹⁵ watt). 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.University Corporation for Atmospheric Research. Hurricanes: Keeping an eye on weather\'s biggest bullies. Retrieved on 2006-03-31.

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.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: What\'s it like to go through a hurricane on the ground? What are the early warning signs of an approaching tropical cyclone?. NOAA. Retrieved on 2006-07-26.

Major basins and related warning centers

Main articles: Tropical cyclone basins, Regional Specialized Meteorological Centre, and Tropical Cyclone Warning Centre

There are six Regional Specialised Meteorological Centres (RSMCs) worldwide. These organizations are designated by the World Meteorological Organization and are responsible for tracking and issuing bulletins, warnings, and advisories about tropical cyclones in their designated areas of responsibility. Additionally, there are six Tropical Cyclone Warning Centres (TCWCs) that provide information to smaller regions.World Meteorological Organization (April 25, 2006). RSMCs. Tropical Cyclone Programme (TCP). Retrieved on 2006-11-05. The RSMCs and TCWCs are not the only organizations that provide information about tropical cyclones to the public. The Joint Typhoon Warning Center (JTWC) issues advisories in all basins except the Northern Atlantic for the purposes of the United States Government.Joint Typhoon Warning Center. Joint Typhoon Warning Center Mission Statement. Retrieved on 2008-02-24. The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) issues advisories and names for tropical cyclones that approach the Philippines in the Northwestern Pacific to protect the life and property of its citizens.Philippine Atmospheric, Geophysical and Astronomical Services Administration. MISSION / VISION. Retrieved on 2008-02-24. The Canadian Hurricane Centre (CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they affect Canada.Canadian Hurricane Centre. Canadian Hurricane Centre. Retrieved on 2008-02-24.

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 the authority of another warning center, Brazilian meteorologists initially treated the system as an extratropical cyclone, although subsequently classified it as tropical.Marcelino, Emerson Vieira; Isabela Pena Viana de Oliveira Marcelino; Frederico de Moraes Rudorff (2004). Cyclone Catarina: Damage and Vulnerability Assessment (PDF). Santa Catarina Federal University. Retrieved on 2006-12-24.

Formation

Main article: Tropical cyclogenesis

Times

Worldwide, 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.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: When is hurricane season?. NOAA. Retrieved on 2006-07-25.

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.McAdie, Colin (May 10, 2007). Tropical Cyclone Climatology. National Hurricane Center. Retrieved on 2007-06-09. 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, tropical cyclone activity begins in late October and ends in May. Southern Hemisphere activity peaks in mid-February to early March.

Factors

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

The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood.Simon Ross. Natural Hazards. Retrieved on 2008-02-24. 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 (79.7 °F) are needed down to a depth of at least 50 metres (160 ft);Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: How do tropical cyclones form?. NOAA. Retrieved on 2006-07-26. waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why do tropical cyclones require 80 °F (27 °C) ocean temperatures to form?. NOAA. Retrieved on 2006-07-25. 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 555 kilometres (345 mi) 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.

Locations

Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Front (ITF),Marine Knowledge Centre. Marine Meteorological Glossary: I. Retrieved on 2008-02-24. the Intertropical Convergence Zone (ITCZ),Philippine Atmospheric, Geophysical and Astronomical Services Administration. Formation of Tropical Cyclones. Retrieved on 2008-02-24. or the monsoon trough.DeCaria, Alex (2005). Lesson 5 – Tropical Cyclones: Climatology.. ESCI 344 – Tropical Meteorology. Millersville University. Retrieved on 2008-02-22. Another important source of atmospheric instability is found in tropical waves, which cause about 85% of intense tropical cyclones in the Atlantic ocean,Avila, Lixion; Richard Pasch (March 1995). "Atlantic tropical systems of 1993" (PDF). Monthly Weather Review 123 (3): 887–896. Retrieved on 2006-07-25.  and become most of the tropical cyclones in the Eastern Pacific basin.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: What is an easterly wave?. NOAA. Retrieved on 2006-07-25.Landsea, Chris (June 1993). "A Climatology of Intense (or Major) Atlantic Hurricanes" (PDF). Monthly Weather Review 121 (6): 1703–1713. Retrieved on 2006-03-25. 

Tropical cyclones move westward equatorward of the subtropical ridge, intensifying as they move. Most of these systems form between 10 and 30 degrees away of the equator,Neumann, Charles J.. Worldwide Tropical Cyclone Tracks 1979-88. Global Guide to Tropical Cyclone Forecasting. Bureau of Meteorology. Retrieved on 2006-12-12. and 87% form no farther away than 20 degrees of latitude, north or south.Henderson-Sellers, H. Zhang, G. Berz, K. Emanuel, William Gray, Christopher Landsea, Greg Holland, J. Lighthill, S-L. Shieh, P. Webster, and K. McGuffie. Tropical Cyclones and Global Climate Change: A Post-IPCC Assessment. Retrieved on 2008-02-25. 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.Neumann, Charles J.. Worldwide Tropical Cyclone Tracks 1979-88. Global Guide to Tropical Cyclone Forecasting. Bureau of Meteorology. Retrieved on 2006-12-12. However, it is possible for tropical cyclones to form within this boundary as Tropical Storm Vamei did in 2001 and Cyclone Agni in 2004.Gary Padgett. Monthly Global Tropical Cyclone Summary, December 2001. Australian Severe Weather Index.Joint Typhoon Warning Center. 1.2 2004 NORTH INDIAN OCEAN TROPICAL CYCLONES. Retrieved on 2008-02-24.

Movement and track

Steering winds

Although 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".Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: What determines the movement of tropical cyclones?. NOAA. Retrieved on 2006-07-25.

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.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: What is an easterly wave?. NOAA. Retrieved on []. 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.DeCaria, Alex (2005). Lesson 5 – Tropical Cyclones: Climatology.. ESCI 344 – Tropical Meteorology. Millersville University. Retrieved on [].

Coriolis effect

Infrared image of Cyclone Monica near peak intensity, showing clockwise rotation due to the Coriolis effect

The Earth\'s rotation imparts an acceleration known as the Coriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents.Baum, Steven K. (January 20, 1997). The Glossary: Cn-Cz.. Glossary of Oceanography and the Related Geosciences with References. Texas A&M University. Retrieved on 2006-11-29. 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.Encyclopædia Britannica. Tropical cyclone: Tropical cyclone tracks. Retrieved on 2008-02-25.

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 westerlies

Storm track of Typhoon Ioke, showing recurvature off the Japanese coast in 2006

When a tropical cyclone crosses the subtropical 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.U. S. Navy. Section 2: Tropical Cyclone Motion Terminology. Retrieved on 2007-04-10. 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 southwesterly winds (blowing northeastward) around a low-pressure system passing over China or Siberia. Many tropical cyclones are eventually forced toward the northeast by extratropical cyclones in this manner, 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.Powell, Jeff, et al. (May 2007). Hurricane Ioke: 20-27 August 2006. 2006 Tropical Cyclones Central North Pacific. Central Pacific Hurricane Center. Retrieved on 2007-06-09.

Landfall

See also: List of notable tropical cyclones and Unusual areas of tropical cyclone formation

Officially, landfall is when a storm\'s center (the center of its circulation, not its edge) crosses the coastline. Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its weakest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a direct hit on the coast. Due to this definition, the landfall area experiences half of a land-bound storm by the time the actual landfall occurs. For emergency preparedness, actions should be timed from when a certain wind speed or intensity of rainfall will reach land, not from when landfall will occur.National Hurricane Center (2005). Glossary of NHC/TPC Terms. National Oceanic and Atmospheric Administration. Retrieved on 2006-11-29.

Multiple storm interaction

Main article: Fujiwhara effect

When 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.USA Today. Fujiwhara effect describes a stormy waltz. Retrieved on 2008-02-21.

Dissipation

Factors

Tropical Storm Franklin, an example of a strongly sheared tropical cyclone in the Atlantic Basin during 2005

A tropical cyclone can cease to have tropical characteristics through several different ways. One such way is if it moves over land, thus depriving it of the warm water it needs to power itself, quickly losing strength.National Hurricane Center. Subject : C2) Doesn\'t the friction over land kill tropical cyclones? Retrieved on 2008-02-25. Most strong storms lose their strength very rapidly after landfall and become disorganized areas of low pressure within a day or two, or evolve into extratropical 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, weakening will accelerate.Bureau of Meteorology. Tropical Cyclones Affecting Inland Pilbara towns. Retrieved on 2008-02-25. Many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall,Yuh-Lang Lin, S. Chiao, J. A. Thurman, D. B. Ensley, and J. J. Charney. Some Common Ingredients for heavy Orographic Rainfall and their Potential Application for Prediction. Retrieved on 2007-04-26. leading to deadly floods and mudslides, similar to those that happened with Hurricane Mitch in 1998.National Hurricane Center (1998). NHC Mitch Report Hurricane Mitch Tropical Cyclone Report. Retrieved on 2006-04-20. Additionally, dissipation can occur if a storm remains in the same area of ocean for too long, mixing the upper 60 metres (200 ft) of water, dropping sea surface temperatures more than 5 °C (41 °F).Joint Typhoon Warning Center. 1.13 Local Effects on the Observed Large-scale Circulations. Retrieved on 2008-02-25. Without warm surface water, the storm cannot survive.Shay, Lynn K., Russell L. Elsberry and Peter G. Black (May 1989). "Vertical Structure of the Ocean Current Response to a Hurricane" (PDF). Journal of Physical Oceanography 19 (5). Retrieved on 2006-12-12. 

A tropical cyclone can dissipate when it moves over waters significantly below 26.5 °C (79.7 °F). 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.Edwards, Jonathan. Tropical Cyclone Formation. HurricaneZone.net. Retrieved on 2006-11-30. 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.Chih-Pei Chang (2004). East Asian Monsoon. World Scientific. ISBN 9812387692.  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.United States Naval Research Laboratory (September 23, 1999). Tropical Cyclone Intensity Terminology. Tropical Cyclone Forecasters\' Reference Guide. Retrieved on 2006-11-30. Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane/typhoon 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 or typhoon-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 are an example of such a windstorm from 1995.Rappaport, Edward N. (November 2, 2000). Preliminary Report: Hurricane Iris: 22 August-4 September 1995. National Hurricane Center. Retrieved on 2006-11-29. 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 dissipation

In 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.Hurricane Research Division. Project STORMFURY. Retrieved on 2008-02-25. The winds of Hurricane Debbie—a hurricane seeded in Project Stormfury—dropped as much as 31%, but Debby regained its strength after each of two seeding forays.H. E. Willoughby, D. P. Jorgensen, R. A. Black, and S. L. Rosenthal. Project Stormfury: A Scientific Chronicle 1962-1983. Retrieved on 2008-02-25. 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.Whipple, Addison (1982). Storm. Alexandria, VA: Time Life Books, 151. ISBN 0-8094-4312-0.  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.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why don\'t we try to destroy tropical cyclones by seeding them with silver iodide?. NOAA. Retrieved on 2006-07-25.

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,Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why don\'t we try to destroy tropical cyclones by placing a substance on the ocean surface?. NOAA. Retrieved on 2006-07-25. 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),Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why don\'t we try to destroy tropical cyclones by cooling the surface waters with icebergs or deep ocean water?. NOAA. Retrieved on 2006-07-25. or blasting the cyclone apart with nuclear weapons.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why don\'t we try to destroy tropical cyclones by nuking them?. NOAA. Retrieved on 2006-07-25. Project Cirrus even involved throwing dry ice on a cyclone.Scotti, R. A. (2003). Sudden Sea: the Great Hurricane of 1938, 1st ed., Little, Brown, and Company, 47. ISBN 0-316-73911-1.  These approaches all suffer from one flaw above many others: tropical cyclones are simply too large for any of the weakening techniques to be practical.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Why do not we try to destroy tropical cyclones by (fill in the blank)?. NOAA. Retrieved on 2006-07-25.

Effects

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

Main article: Effects of tropical cyclones

Tropical cyclones out at sea cause large waves, heavy rain, and high winds, disrupting international shipping and, at times, causing shipwrecks.David Roth and Hugh Cobb (2001). Eighteenth Century Virginia Hurricanes. NOAA. Retrieved on 2007-02-24. Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favourable for subsequent tropical cyclones. On land, strong winds 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.James M. Shultz, Jill Russell and Zelde Espinel (2005). Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development. Oxford Journal. Retrieved on 2007-02-24. 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.Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. Frequently Asked Questions: Are TC tornadoes weaker than midlatitude tornadoes?. NOAA. Retrieved on 2006-07-25.

Over the past 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.Staff Writer. "Hurricane Katrina Situation Report #11" (PDF), Office of Electricity Delivery and Energy Reliability (OE) United States Department of Energy, 2005-08-30. Retrieved on 2007-02-24. 

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 on 2006-05-02. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes and polar regions.Living With an Annual Disaster. Zurich Financial Services (July/August 2005). Retrieved on 2006-11-29. 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.Christopherson, Robert W. (1992). Geosystems: An Introduction to Physical Geography. New York: Macmillan Publishing Company, 222–224. ISBN 0-02-322443-6. 

Observation and forecasting

Observation

Main article: Tropical cyclone observation

Sunset view of Hurricane Isidore\'s rainbands photographed at 7,000 feet (2.1 km)

Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and weather stations, being relatively sparse, are rarely available on the site of the storm itself. Surface observations are generally available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Usually, real-time measurements are 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.Florida Coastal Monitoring Program. Project Overview. University of Florida. Retrieved on 2006-03-30.

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 by showing a storm\'s location and intensity every several minutes.Central Pacific Hurricane Center. Observations. Retrieved on 2006-12-09.

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