TROPICAL CYCLONE FACTS & FIGURES

This page has been updated February 18, 2001

The "Atlantic Tropical Cyclone Quick Reference Guide", began in 1992 after hurricane Andrew as five pages in a notebook with several statistics and sketches. It grew to 15 pages in 1993 and 27 in 1994. Originally it was intended as a personal guide to the tropics to look up quick facts and statistics on Atlantic Tropical Systems. In 1994 as I entered college and bought a computer, I decided to copy the hand written guide to a neater, better organized guide book. This allowed me to update the guide frequently and it also allowed the guide to grow. Then several of my friends as school suggested I make copies of the guide and sell it. In February, 1995, I had compiled 57 pages and sold several copies. Since then the guide has been updated continuously and is currently being updated for the year 2001.

Tropical Definitions
Characteristics of Storms                               
Formation Areas
Tropical Cyclones around the World
Atlantic Tropical Season
Development Criteria for Tropical Cyclones
Tropical Cyclone Dissipation
Tropical Cyclone Formation
Beginning Dates of Tropical Cyclones
Years with Least Number of Tropical Cyclones
Years with Greatest Number of Tropical Cyclones
Retired Hurricane Names
Land falling Hurricanes or Tropical Storms U.S. 1990-1995
Land falling Hurricanes or Tropical Storms U.S. 1886-1995
The Saffir-Simpson Scale
The Saffir Simpson Scale Chart
The Most Intense Hurricane to Hit the U.S. 1900-1995

TROPICAL DEFINITIONS

Tropical Low

Tropical Wave

A weak area of low pressure without a defined closed circulation, that normally moves westward off the coast of coast of Africa. About 65 waves track across the Atlantic each year.

Tropical Disturbance

Tropical Depression

A tropical low with a closed surface circulation with a wind speed less than 39 mph (35 kts).

Tropical Storm

A tropical low with a closed circulation and winds greater than 38 mph (35 kts).

Hurricane

A tropical low with wind speeds greater than 73 mph (64 kts).

Extratropical Storm

The dissipative stages of a tropical cyclone as it loses it tropical characteristics. Also an extratropical storm can be any low pressure system. (see characteristics). No wind criteria given with these storms.

Subtropical Depression

Subtropical Storm

A hybrid of an extratropical storm and a tropical storm. Wind speed is greater than 38 mph. In most cases if the winds exceed 73 mph the system is classified as a hurricane.

CHARACTERISTICS OF STORMS

Tropical Cyclones

Extratropical Cyclones

I.

II.

Subtropical Cyclone

I. An upper level cold low with a circulation extending to the surface and maximum sustained winds generally occurring at a radius of about 100 miles or more from the pressure center.

II. A mesoscale cyclone originating in or near a frontolyzing zone of horizontal wind shear, with radius of maximum sustained winds generally less than 30 miles. The entire circulation sometimes encompasses an area initially no more than 100 miles in diameter. These are generally short lived cyclones which may vary in structure from cold to warm core.

Figure . a.) Surface analysis chart b,) 850 mb analysis chart c.) 500 mb analysis; from 1200 UTC, November 18, 1996 showing a subtropical storm of type I off the northeast coast of the United States. This storm initially started as a cold core cut off upper low and was a peaked as a 982 mb extratropical cyclone, then stalled over the Gulf Stream waters and developed subtropical characteristics.

Figure 8. Satellite image of the above Subtropical cyclone taken at 1015 UTC, November 18, 1996. Note the similar cloud characteristics to that of a tropical cyclone.

Figure 9. Surface analysis chart from 1200 UTC, June 1, 1997 showing a subtropical storm of type II off the coast of North Carolina. The subtropical storm initially started as a weak low pressure area off the coast of Florida and tracked northward. The subtropical storm was on the eastern edge of a large surface and upper level low pressure system over Eastern Tennessee. .

Figure 10. Satellite image of the above Subtropical cyclone taken at 1400 UTC, June 1, 1997 Note the small circulatlon and similar cloud characteristics to that of a tropical cyclone.

In both cyclone types wind speeds will normally range from 30 to 72 mph. In most cases if the maximum sustained wind exceeds 73 mph, it will be classified as a tropical hurricane. Although if tropical characteristics are not present it will remain subtropical.

Click here for more info on Subtropical Cyclones and a history.

FORMATION AREAS OF TROPICAL CYCLONES

Atlantic Basin

May  In the month of May, if a tropical cyclone were to form it would be in the Eastern Gulf of Mexico or the North west Caribbean Sea. It is here in this region that the seas surface temperatures have risen above 80 degrees F. In the Eastern Gulf, wind shear is still strong at this time of year. Occasionally a weak trough or drier air has a tendency to reside here
in May and limit tropical cyclone activity.

 

June In June there is expansion of the formation areas. Upper-level winds have relaxed some over the Gulf of Mexico as also begin to rise.

 

 

 

July In July, the eastward expansion of the formation area's towards the Bahamas and east of the Lesser Antilles. The extension into the Bahammas is due to the warming of the Gulf Stream and shallow waters nearby. The warming off of the Lesser Antilles is due to the direct sunshine, this strip usually does not warm though climatologically until the latter part of July.

 

 

August  In August 80 degree or warmer water temperatures stretches from Texas to the Cape Verde Islands near the coast of Africa. Warm water has made its way north to Cape Hatteras back towards Bermuda. The warming in the Cape Verde region is usually delayed until the middle of the month.

September  The first part of September sees an area of approximately 70,000 square miles of ocean prime for tropical development. The tracks of the storms the formation boundaries and travel thousands of miles. One may notice the region of the Eastern Caribbean throughout these graphics. This region is usually not favorable for development during any time of the
season. If a tropical cyclone were to form east of the islands, it would survive in this region but remain status quo until it reached the Western Caribbean. The reason for this is not totally understood, but there may be a weak current that allows for upwelling of cooler water temperatures and wind shear created by the mountains of South America.

OctoberOctober sees a major cut in the formation areas, especially in the Eastern Atlantic. By this time of the year, the upper level wind pattern has shifted back to its winter time position. The waters off the east coast of the United States have constricted further south and the western Gulf of Mexico has become hostile with upper level winds and drier air as many
cold fronts and troughs move into the region.

November  November- The last month of the hurricane season, the area is very restricted to the Southwest Caribbean Sea as this is the only region that is not effected by upper-level wind shear. Water temperatures have cooled significantly as the Northern Hemisphere approaches the Winter Solstice.
 

Other Formation Areas

TROPICAL CYCLONES AROUND THE WORLD

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THE ATLANTIC TROPICAL SEASON

DEVELOPMENT CRITERIA FOR TROPICAL CYCLONES

Observations have shown that the necessary conditions for the development of tropical cyclones generally are:

TROPICAL CYCLONE DISSIPATION

A tropical cyclone will not dissipate unless the following conditions occur.

Beginning Dates of Tropical Cyclones   1886 to 2000  (up to Florence)

114 Years - 984 Storms and Hurricanes

This table includes only tropical cyclones which attained Tropical Storm or Hurricane strength, however the beginning dates that are given are the date the disturbance gained tropical classification.

This table is to show the frequency of tropical cyclone activity in the Atlantic basin for each of the ten day period given. A graph of this chart is available

Years with the Least Number of Tropical Cyclones

* This is the Greatest Number of Tropical Cyclones recorded Atlantic. ** 1995 was the second busiest season in the Atlantic Basin since 1933. It was also the first year the letter "T" was used to designate a storm name. Tropical Depressions are NOT included in the count.

Retired Hurricane Names 1979-2000

Whenever a hurricane has had a major impact, any country affected by the storm can request that the name of the hurricane be "retired" by agreement of the World Meteorological Organization (WMO). Retiring a name actually means that it cannot be reused for at least 10 years, to facilitate historic references, legal actions, insurance claim activities, etc. and avoid public confusion with another storm of the same name. If that happens, a like gender name is selected in English, Spanish or French for Atlantic Storms.

Atlantic Hurricane Names 2001-2006
 

Landfalling Hurricanes or Tropical Storms U.S. 1990-1999
 
 

*** A Tropical Cyclone Can Make Multiple Landfalls

Landfalling Hurricanes or Tropical Storms U.S. 1886-2000

 *New Hampshire has not been directly hit by a tropical cyclone on it's 7 mile wide Atlantic coast. **In 1991 Hurricane Bobs' eye passed directly over Block Island, Rhode Island, constituting a landfall

The Saffir-Simpson Scale

Category 2 Winds of 96 to 110 miles per hour. Considerable damage to shrubbery and tree foliage; some trees blown down. Major damage to exposed mobile homes. Extensive damage to poorly constructed signs. Some damage to roofing materials or buildings; some window and door damage. No major damage to buildings. And/or storm surge of 6 to 9 feet above normal. Coastal roads and low lying escape routes inland cut off by rising water 2 to 4 hours before arrival of hurricane center. Considerable damage t piers. Marina's flooded. Small craft in unprotected anchorage's torn from moorings. Evacuation of some shoreline residents and low-lying islands areas required

Category 3 Winds of 111 to 130 mph. Storm surge generally 9-12 ft above normal. Some structural damage to small residences and utility buildings with a minor amount of wall failures. Damage to shrubbery and trees with foliage blown off trees and large tress blown down. Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane center. Flooding near the coast destroys smaller structures with larger structures damaged by battering of floating debris. Terrain continuously lower than 5 ft above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying residences with several blocks of the shoreline may be required.

Category 4 Winds 131 to 155 mph. Storm surge generally 13-18 ft above normal. More extensive wall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape routes may be cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles.

Category 5 Winds greater than 155 mph (135 kts or 249 kph). Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles of the shoreline may be required. 

The Saffir-Simpson Hurricane Scale Chart

The Most Intense Hurricanes to Strike the U.S. 1900-1995

The intensity of a hurricane is determined by it central pressure and not its wind speed
* Pressure and intensity guide are given for the time when the hurricane made landfall on the U.S. coastline. The hurricane may have been stronger prior to landfall.