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A tropical cyclone is a storm system characterized by a low pressure center and numerous thunderstorms that produce strong winds 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 term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropicalMaritime Tropical air masses. The term "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 other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression and simply cyclone.

"It's not if, but when severe weather or a hurricane will threaten where you live"
Barometer Bob Brookens

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 40 kilometres 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.

Warning Centres

There are six Regional Specialized 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. 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. 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. The Canadian Hurricane Centre (CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they affect Canada.

Hurricane Formation

Hurricane Season

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.

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 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.

Formation

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 are needed down to a depth of at least 50 metres; 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 555 kilometers 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.

Birth Place

Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Front (ITF), 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 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, 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 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".

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 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.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 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

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

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. 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.

Landfall

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.Multiple storm interaction

Multiple storm interaction

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.

Dissipation

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. 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. 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 60 metres of water, dropping sea surface temperatures more than 5 °C . 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/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. 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.

Hurricane Names

Experience shows that the use of short, distinctive given names in written as well as spoken communications is quicker and less subject to error than the older more cumbersome latitude-longitude identification methods. These advantages are especially important in exchanging detailed storm information between hundreds of widely scattered stations, coastal bases, and ships at sea.

Since 1953, Atlantic tropical storms have been named from lists originated by the National Hurricane Center. They are now maintained and updated by an international committee of the World Meteorological Organization. The original name lists featured only women's names. In 1979, men's names were introduced and they alternate with the women's names. Six lists are used in rotation. Thus, the 2008 list will be used again in 2014. Here is more information about the history of naming hurricanes.

For more information regarding NOAA and the Hurricane naming, click here.

2008	2009	2010	2011	2012	2013
Arthur Bertha Cristobal Dolly Edouard Fay Gustav Hanna Ike Josephine Kyle Laura Marco Nana Omar Paloma Rene Sally Teddy Vicky Wilfred	Ana Bill Claudette Danny Erika Fred Grace Henri Ida Joaquin Kate Larry Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda	Alex Bonnie Colin Danielle Earl Fiona Gaston Hermine Igor Julia Karl Lisa Matthew Nicole Otto Paula Richard Shary Tomas Virginie Walter	Arlene Bret Cindy Don Emily Franklin Gert Harvey Irene Jose Katia Lee Maria Nate Ophelia Philippe Rina Sean Tammy Vince Whitney	Alberto Beryl Chris Debby Ernesto Florence Gordon Helene Isaac Joyce Kirk Leslie Michael Nadine Oscar Patty Rafael Sandy Tony Valerie William	Andrea Barry Chantal Dorian Erin Fernand Gabrielle Humberto Ingrid Jerry Karen Lorenzo Melissa Nestor Olga Pablo Rebekah Sebastien Tanya Van Wendy

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Hurricane Related Communications

Hurricane Hunters

Hurricane Hunters are aircraft that fly into tropical cyclones in the North Atlantic Ocean and Northeastern Pacific Oceanweather data in and around those storms. In the Western Pacific OceanIndian Ocean, the titles of Typhoon Chasers (Air Force) or Typhoon Trackers (Navy) are used for these organizations. In the United States, the Air Force, Navy, and NOAA units have all participated in this mission.

The 53rd Weather Reconnaissance Squadron, better known as the “Hurricane Hunters,” is a United States Air Forcesquadron of aircraft, based in Biloxi, Mississippi, that flies missions into hurricanes and weather systems for research purposes and observation.

The Hurricane Hunters of the Air Force Reserve are distinct from the NOAA Hurricane Hunters, based at the Aircraft Operations Center at MacDill AFB, in Tampa, Florida using WP-3D Orion and Gulfstream IV-SP aircraft for this mission.

The NOAA Hurricane Hunters mainly perform surveillance, research, and reconnaissance with highly instrumented aircraft including airborne Doppler radar measurements in both Atlantic and Pacific storms.

Although satellite data has revolutionized weather forecasters' ability to detect early signs of tropical cyclones before they form, there are still many important tasks is not suited for. Satellites cannot determine the interior barometric pressure of a hurricane, nor provide accurate wind speed information. These data are needed to accurately predict hurricane development and movement.

Because satellites cannot collect the data and ships are too slow and vulnerable, the only viable way to collect this information is with aircraft. The 53rd Weather Reconnaissance Squadron “Hurricane Hunters” flies instrumented WC-130J aircraft into storms to collect the required meteorological data. The area of responsibility for the “Hurricane Hunters” is midway through the Atlantic Ocean to the Hawai’ian Islands. The Air Force Reserve Hurricane Hunters have also been tasked to fly into typhoons in the Pacific Ocean on occasion, as well as gather data in winter storms.

Hurricane Hunter Frequencies

• 3407.0 National Hurricane Center air-gnd "ALPHA"
• 4724.0 Hurricane hunter acft - GHFS
• 5562.0 National Hurricane Center air-gnd "BRAVO"
• 5610.0 National Hurricane Center air-gnd "CHARLIE"
• 6673.0 National Hurricane Center air-gnd "DELTA"
• 6739.0 Hurricane hunter acft-GHFS guarded by MacDill & Ascension
• 8876.0 National Hurricane Center air-gnd "ECHO"
• 8968.0 Hurricane hunter acft - GHFS
• 8992.0 Hurricane hunter acft - GHFS guarded by MacDill & Ascension
• 10015.0 National Hurricane Center air-gnd "FOXTROT"
• 11175.0 Hurricane hunter acft - GHFS guarded by MacDill & Ascension
• 13200.0 Hurricane hunter acft - GHFS
• 13267.0 National Hurricane Center air-gnd "GOLF"
• 15016.0 Hurricane hunter acft - GHFS guarded by MacDill & Ascension
• 17901.0 National Hurricane Center air-gnd "HOTEL"
• 17976.0 Hurricane hunter acft - GHFS
• 21937.0 National Hurricane Center air-gnd "INDIA"

Hurricane reconnaissance aircraft now operate primarily on U.S. Global High Frequency System (GHFS) frequencies. Best frequencies to monitor are those guarded by McDill and Ascension. After initial contact on one of the published GHFS frequencies, listen closely for them to switch to a non-published discrete frequency to pass traffic. Aircraft call signs are "GULL-nn" or "TEAL-nn" (where nn is a 2-digit number), and "NOAA-42" and "NOAA-43." The GULL and TEAL aircraft are type WC-130 based at Keesler AFB, Biloxi, MS. The NOAA aircraft are type WP-3D based at MacDill AFB, Tampa, FL. Look for the new NOAA Gulfstream IV-SP (tail number N49RF, call sign "NOAA-49") tomake its debut this season.

Amateur Emergency Nets in Hurricane Areas

Whenever a hurricane is within 300 miles of land in the northern western hemisphere, the Hurricane Watch Net is operational on 14325. The Hurricane Watch Net provides communication between the National Hurricane Center and the affected areas.

Below are other area net frequencies (frequencies in kHz - Mode: USB or LSB).

• Alabama 3695.0
• Antilles 7165.0
• Southern LA 7245.0
• Baja 7235.0
• Belize 3935.0 7250.0
• Bermuda 14275.0
• Caribbean Emergency 14185.0
• Caribbean Maritime Mobile 7115.0
• Caribean WX 3808.0
• California WX 3948.0
• Georgia 3975.0
• Gulf Coast Central Hurr. 3935.0 7245.0
• Gulf Coast West Hurr. 3845.0 7260.0
• Gulf Coast (Outgoing only) 3967.0 7283.0
• Gulf Coast WX 3995.0 7290.0
• Gulf Coast Health and Welfare 3993.5 7264.0
• Interamericas H&W 21390.0
• Lake Charles, LA 3993.5 7264.0
• Louisiana 14340.0 (1900Z)
• Manana 7070.0
• Mexican National 3987.5
• Mississippi ARES 3923.0 3910.0
• North Carolina 3915.0
• South Carolina 3915.0
• South Texas Emergency 3955.0
• Texas Emergency 7240.0 7250.0
• Texas Traffic/H&W 3691.0 7290.0 day 3910.0 night
• Transatlantic Maritime Mobile 21400.0
• Waterway 7268.0

During a communications emergency, W1AW transmits special voice bulletins on the hour on 01855, 03990, 07290, 14290, 18160, 21390 and 28590.

The National Institute of Standards and Technology broadcasts storm warnings on 2.5, 5, 10, 15 & 20 MHz AM according to the following schedule:

• WWV hh:08
• WWVH hh:38

Thanks goes to Wikipedia, Barometer Bob Brookens, Environment Canada and The Weather Network for content, information and help.

 

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