August 5, 2008
COLORADO STATE HURRICANE FORECAST TEAM INCREASES FORECAST SLIGHTLY, CONTINUES TO PREDICT VERY ACTIVE SEASON
FORT COLLINS - The Colorado State University hurricane team today increased the number of storms expected to form in the Atlantic this season based on warm sea surface temperatures and low sea level pressures observed over the tropical Atlantic in June and July, combined with an active early season in the deep tropics.
Researchers Philip Klotzbach and William Gray expect a much more active season than the typical season between 1950 and 2000. They are calling for a total of 17 named storms for the entire hurricane season with nine becoming hurricanes and five becoming intense hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.
This early August forecast raises the team's early June prediction of 15 named storms, eight hurricanes and four intense hurricanes. The Net Tropical Cyclone activity prediction has been raised to 190 percent from 160 percent in early June. The long-term (1950-2000) average is 9.6 named storms, 5.9 hurricanes, 2.3 intense hurricanes and 100 percent Net Tropical Cyclone activity per year.
Five named storms have been observed so far this season including Hurricane Bertha, which was the longest-lived tropical cyclone that has ever formed during July, and Hurricane Dolly, which made landfall as a Category 2 hurricane in south Texas on July 23.
"We have increased our forecast because there has already been a very active early tropical cyclone season in the deep tropics and more favorable hurricane-enhancing sea surface temperature and sea level pressure patterns in the tropical Atlantic have developed," said Phil Klotzbach, lead author of the forecasts. "The primary concern with our current very active seasonal forecast numbers is the continued ocean surface warming in the eastern and central tropical Pacific. Although it seems unlikely at this point, there is a possibility that a weak El Nino could develop by the latter part of the hurricane season. If this happened, it would likely reduce the number of late season tropical cyclones."
This is Colorado State's 25th year of issuing early August forecasts. The team has correctly predicted an above- or below-average season in 21 of 24 years for named storms and 17 of 24 years for hurricanes in their early August forecasts.
"We expect the Atlantic basin tropical cyclone season will be very active with activity that is about 190 percent of the long-term average," said Gray. "We base our predictions on long-period statistical models constructed on the past 60 years of historical data. Residents should take these forecasts as an indication of what this year's hurricane activity is likely to be if the global atmosphere and ocean behave in the next few months as they have over the last 60 years. No seasonal forecasts can determine when or where storms are going to strike, so coastal residents should take precautions during hurricane season and be prepared."
The hurricane forecasters on Tuesday also issued a forecast for tropical cyclone activity during the month of August. The monthly forecasts use different parameters than the seasonal forecasts to predict storm activity within shorter time periods.
For the month of August, the team expects four named storms, three hurricanes and one intense hurricane for the Atlantic basin. This activity is approximately 180 percent of the average activity expected during the month of August.
"The same factors that make individual months active or inactive are often not the same factors that make the entire season active or inactive," said Klotzbach. "We are continually improving our forecasts to provide people with specific monthly hurricane forecasts along with landfall probability forecasts."
Along with today's seasonal and August monthly forecast, the team has updated the Landfall Probability Web site, which provides probabilities of tropical storm-force, hurricane-force and intense hurricane-force winds impacting specific locations along the U.S. East and Gulf coasts for the remainder of the hurricane season.
Probabilities are available for 11 regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. The Web site, available to the public at http://www.e-transit.org/hurricane, is an Internet tool that adjusts landfall probabilities for regions and counties based on the current climate and its projected effects on the remainder of the hurricane season. Klotzbach and Gray, with assistance from the GeoGraphics Laboratory at Bridgewater State College in Massachusetts, launched the site in 2004.
The Colorado State forecast team continues to warn of the considerably higher-than-average probability of at least one intense (or major) hurricane making landfall in the United States for the remainder of this year's hurricane season. According to today's forecast, there is a 67 percent chance of an intense hurricane hitting somewhere along the U.S. coastline (long-term average is 52 percent). For the U.S. East Coast, including the Florida Peninsula, the probability of an intense hurricane making landfall is 43 percent (long-term average is 31 percent). For the Gulf Coast from the Florida Panhandle westward to Brownsville, Texas, the probability is 42 percent (the long-term average is 30 percent). The forecast also calls for above-average major hurricane landfall risk in the Caribbean.
Gray said the United States has been fortunate over the past few decades in experiencing only a few major hurricanes making landfall in Florida and along the East Coast. Between 1995 and 2003, 122 named storms, 69 hurricanes and 32 major hurricanes formed in the Atlantic basin. During that period, only three of the 32 major hurricanes - Opal, Bret and Fran - crossed the U.S. coastline. Based on historical averages, about one in 3.5 major hurricanes comes ashore in the United States.
In 2004 and 2005, 13 major hurricanes formed in the Atlantic basin - seven of them striking the U.S. coast. In 2004, Hurricanes Charley, Ivan and Jeanne made landfall followed in 2005 by Dennis, Katrina, Rita and Wilma.
"Those years were anomalies," Gray said. "We are in an active cycle in the Atlantic basin that is expected to last another 15 to 20 years. We believe this is part of a natural ocean cycle and is not the result of human-induced increases in atmospheric carbon dioxide."
The team will issue seasonal updates of 2008 Atlantic basin hurricane activity on Sept. 2 and Oct. 1. A forecast for the month of September will be included with the Sept. 2 update, while a forecast for the month of October will be included with the Oct. 1 update.
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