Published: 2006-05-31 16:28:00
Updated: 2006-05-31 16:28:00
Posted May 31, 2006
As we start the hurricane season it is a good idea to get an understanding of where tropical systems form during the six month period. As ocean temperatures rise and upper level winds lessen, the vicinity where these storms grow changes.
The following graphics below illustrate very well what regions of the Atlantic Basin are more prone to storm formation during certain times of the season and which areas are more prone to a landfalling cyclone.
These images and information are courtesy of NOAA and Wikipedia.
JUNE:The beginning of the hurricane season is most closely related to the timing of increases in sea surface temperatures, convective instability, and other thermodynamical factors. Although this month marks the beginning of the hurricane season, the month of June generally still sees little activity, with an average of about 3 tropical systems per 5 years. Any tropical systems usually form in the Gulf of Mexico or off the east coast of the United States.
July still has relatively little activity, with about one tropical cyclone a year. Climatologically speaking, half of seasons have their first tropical storm by July 11 with a second by August 8, using data from 1944 to 1996.
Formation usually occurs in the eastern Caribbean Sea around the Lesser Antilles, in the north and east parts of the Gulf of Mexico, in the northern Bahamas, and off the coast of The Carolinas and Virginia. Storms travel west through the Caribbean and then either move more northerly and curving near the eastern coast of the U.S. or southerly and entering the Gulf of Mexico.
Activity increases significantly in August, with an average of about 2.8 storms per year. About half of seasons have four named systems and one hurricane total by August 30. The average season also sees one major hurricane by September 4.
The peak of the hurricane season in September corresponds to a time with low wind shear and high sea surface temperatures. The month of September sees an average of 3.6 storms a year. By September 24, the average season sees 7 named systems, of which 4 are hurricanes. In addition, two major hurricanes would be seen by September 28.
The favorable conditions found during September begin to decay in October. The main reason for the decrease in activity is increasing wind shear, although sea surface temperatures are also usually cooler than in September. Activity falls off markedly, with 1.8 cyclones developing in an average season. By October 21, the average season is expected to have 9 named storms with 5 hurricanes. A third major hurricane would be expected sometime between September 28 and the end of the year for half of all seasons.
Although tropical activity is lower than in September, another small peak in activity occurs around October 20.
Wind shear from westerlies increases substantially through November, generally preventing cyclone formation. On average, one storm forms during November every other year.