Posted on 05 Aug 2010
The Colorado State University hurricane team on Wednesday maintained its prediction for an above-average 2010 Atlantic hurricane season based on unusually warm tropical Atlantic sea surface temperatures and the development of La Nina.
For the August forecast, the team stuck with its June prediction of 18 named storms forming in the Atlantic basin between June 1 and Nov. 30. Ten of the storms are predicted to become hurricanes, and of those 10, five are expected to develop into major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.
“The probability of a major hurricane making landfall along the U.S. coastline is 75 percent compared with the last-century average of 52 percent,” said William Gray, in his 27th year of forecasting hurricanes at Colorado State. “We have witnessed the development of La Nina conditions over the past couple of months, and we believe that a moderate La Nina will be present over the next several months, which is associated with decreased levels of vertical wind shear and increased hurricane activity.”
“We’ve also noted the persistence of anomalously warm sea surface temperatures in both the tropical and North Atlantic and low sea level pressures that have occurred across the tropical Atlantic in June and July,” said Phil Klotzbach, lead author on the forecast. “These very warm waters are associated with dynamic and thermodynamic factors that are very conducive for an active Atlantic season.”
The team also updated its U.S. landfall probabilities. These probabilities are calculated based upon 20th century landfall statistics and then adjusted by the latest seasonal forecast.
The hurricane forecast team's probabilities for a major hurricane making landfall on various portions of the U.S. coast:
- A 50 percent chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida Peninsula (the long-term average is 31 percent).
- A 49 percent chance that a major hurricane will make landfall on the Gulf Coast from the Florida Panhandle west to Brownsville (the long-term average is 30 percent).
-A 64 percent chance that a major hurricane will make landfall in the Caribbean and Central America (the long-term average is 42 percent).
The team also debuted a forecast for Caribbean basin activity this year. The Caribbean looks to be very active in 2010, with overall tropical cyclone activity in the Caribbean approaching levels experienced in 2004 and 2005.
Probabilities of tropical storm-force, hurricane-force and major hurricane-force winds occurring at specific locations along the U.S. East and Gulf Coasts within a variety of time periods are listed on the forecast team's Landfall Probability Web site. The site provides U.S. landfall probabilities for 11 regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. Probabilities for each coastal state are available.
The website, at http://www.e-transit.org/hurricane, adjusts landfall probabilities for regions, states, and counties based on the current climate and its projected effects on the upcoming hurricane season. Klotzbach and Gray update the site regularly with assistance from the GeoGraphics Laboratory at Bridgewater State College in Massachusetts. In addition, probabilities for various islands in the Caribbean and landmasses in Central America are now available on the Landfall Probability Web site.
Currently observed climate factors are similar to conditions that occurred during 1952, 1958, 1998 and 2005 seasons. The average of these four seasons had well above-average activity, and Klotzbach and Gray predict the 2010 season will have activity in line with the average of these five years.
The hurricane forecast team predicts tropical cyclone activity in 2010 will be 195 percent of the average season. By comparison, 2009 witnessed tropical cyclone activity that was about 69 percent of the average season.
The Colorado State forecasts are based on the premise that global oceanic and atmospheric conditions - such as El Nino, sea surface temperatures and sea level pressures - that preceded active or inactive hurricane seasons in the past 60 years provide meaningful information about similar trends in future seasons.