Yesterday (30 November 2008) signaled the end of the official 2008 hurricane season in both the North Atlantic basin (which includes the Gulf of Mexico and the Caribbean) and the Eastern North Pacific basin, a region extending from the western coast line of North America westward to a longitude of 140 degrees west. While a hurricane or other tropical cyclone may develop after 30 November, such an event is rare. In the North Atlantic, the latest recorded hurricane was on 31 December 1954 and the earliest was on 7 March 1908.
After what appeared as a quiet 2007 hurricane season in the North Atlantic, 2008 was considerably more active, primarily because of the record number of hurricanes and tropical storms that approached the US during this just-concluded 2008 Atlantic hurricane season. When compared with the long-term averages, the season was more active than average, with sixteen tropical cyclones becoming named systems in the North Atlantic in 2008. Of these 16 systems, eight developed into hurricanes (with maximum sustained winds in excess of 74 mph), and five becoming major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Intensity Scale).
The first tropical system of the season was Tropical Storm Arthur that formed over the waters of the western Caribbean offshore of Belize and Mexico's Yucatan Peninsula on 31 May 2008. As of this writing, the last tropical cyclone was Hurricane Paloma, which formed on 5 November over the Caribbean and dissipated over Cuba on 10 November. The five major hurricanes were Hurricanes Bertha, Gustav, Ike, Omar, and Paloma. Six consecutive tropical cyclones (Hurricane Dolly, Tropical Storms Edouard and Fay, and Hurricanes Gustav, Hanna and Ike) made landfall on the US mainland, which was record. Three major hurricanes (Hurricanes Gustav, Ike and Paloma) made land fall along the Cuban coast, which also represented a record. Also noteworthy was the occurrence of at least one major hurricane in five consecutive months.
Additional information concerning individual tropical cyclones during this season can be found at http://www.nhc. noaa.gov/2008atlan.shtml. More details should appear late next week, as the final version of the North Atlantic summary is prepared.
In the eastern North Pacific, the hurricane season runs from 15 May to 30 November. The 2008 hurricane season had 16 named tropical systems, with six reaching hurricane status. In addition, two tropical depressions formed in the basin. Hurricanes Hernan and Norbert became a major hurricanes. Tropical Storm Alma made landfall along the Central American coast, while Tropical Storms Julio and Lowell, along with Hurricane Norbert made landfall along the Mexican coast. For additional information concerning some of these tropical cyclones, see http://www.nhc.noaa.gov/2008epac.shtml. More details should be forthcoming in the Eastern North Pacific summary.
While the 16 named tropical cyclones and eight hurricanes so far during the 2008 North Atlantic hurricane season was below the record 2005 season, the numbers were above the long-term average in the Atlantic Basin. Using long term averages running from 1931 to 2007, a typical North Atlantic hurricane season would have slightly more than 10 named systems, with nearly 6 hurricanes and 4 tropical storms. The 2005 season had 28 named systems, with 13 being classified as hurricanes and 8 tropical storms. The least active in recent history was 1982 when only five named tropical cyclones were reported (two hurricanes and three tropical storms). Hurricane forecasters at NOAA's Climate Prediction Center suggest that the reason for the very active Atlantic hurricane season was a combination of several factors that included a the phase of a multi-decadal signal that favored increased hurricane activity; a lingering La Niña event; and above average tropical Atlantic sea surface temperatures at the height of hurricane season. [NOAA News]
Hurricane experts, Professor William Gray from Colorado State University in Fort Collins has been issuing long-range hurricane forecasts for more than two decades. During the last two years, his associate, Philip Klotzbach, has become the lead forecaster. Their forecasts are based upon several factors that include analysis of the wind field at several levels, the rainfall over West Africa and the effects of El Niño. In December 2007, the group predicted that the 2008 season would be quite active with more cyclones than the average (1950-2000) season. The forecasters expected the large number as the current La Niña conditions begin to weaken. They also anticipated an above-average probability of a landfall on the mainland US. In subsequent updates in April, June and August of 2008, they revised their forecasts upward to 17 named cyclones, nine hurricanes and five major hurricanes. For additional information on these forecasts refer to http://typhoon.atmos.colostate.edu/forecasts/. They should issue a forecast for 2009 near the end of this upcoming week.
The 2008 season in the eastern North Pacific was slightly more active than average, as the year's number of named systems was one more than the long-term (1966-2007) average of 15 named tropical cyclones. The seven hurricanes compare with the eight tropical cyclones that typically reach hurricane status over the last 42 years.
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Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
© Copyright, 2008, The American Meteorological Society.