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In August, both the Colorado State University (CSU) Hurricane Forecast Team and the National Oceanic and Atmospheric Administration (NOAA) increased their predictions for hurricanes for the remainder of the 2008 season.
With five named storms, one major hurricane and one Cat. 2 hurricane already in the books, both services increased their predictions and probabilities based on conditions across the Atlantic Basin that favor storm development and strong early season activity.
In early August, CSU researchers Philip Klotzbach and William Gray began calling for a total of 17 named storms for the entire hurricane season with nine becoming hurricanes and five becoming intense hurricanes (Category 3, 4, 5) with sustained winds of 111 mph or greater. This forecast raised the team’s early June prediction of 15 named storms, eight hurricanes and four intense hurricanes.
Days later, NOAA projected an 85 percent probability of an above-normal season—up from 65 percent in May. The updated outlook included a 67 percent chance of 14 to 18 named storms, of which seven to 10 are expected to become hurricanes, including three to six major hurricanes. These ranges encompass the entire season, which ends November 30, and include the five storms that have formed thus far this season.
HIGHER-THAN-AVERAGE LANDFALL PROBABILITY
By the end of July, two hurricanes had already formed and threatened the U.S. cost. Hurricane Bertha was the longest-lived tropical cyclone that has ever formed during July, and Hurricane Dolly made landfall as a Category 2 hurricane in south Texas on July 23, both the CSU team and NOAA reported.
“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 CSU 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.”
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 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.”
The team also updated its 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.
The Colorado State forecast team continued 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 its August 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, TX, 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.
BE PREPARED
In May, NOAA’s outlook called for 12 to 16 named storms, including six to nine hurricanes and two to five major hurricanes. An average Atlantic hurricane season has 11 named storms, including six hurricanes and two major hurricanes. NOAA upped its probabilities in August based on a number of factors.
“Leading indicators for an above-normal season during 2008 include the continuing multi-decadal signal—atmospheric and oceanic conditions that have spawned increased hurricane activity since 1995—and the lingering effects of La Niña,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center. “Some of these conditions include reduced wind shear, weaker trade winds, an active West African monsoon system, the winds coming off of Africa and warmer-than-average water in the Atlantic Ocean.”
Another indicator favoring an above-normal hurricane season is a very active July, the third most active since 1886. Even so, there is still a 10 percent chance of a near normal season and a five percent chance of a below normal season, NOAA reported.
The Atlantic hurricane season includes activity over the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. The peak months of the season are August through October. NOAA’s hurricane outlook is a general guide to the expected level of hurricane activity for the entire season. NOAA does not make seasonal landfall predictions because hurricane landfalls are largely determined by the weather patterns in place as a hurricane approaches.
“It is critical that everyone know the risk for your area, and have a plan to protect yourself, your family and your property, or to evacuate if requested by local emergency managers. Be prepared throughout the remainder of the hurricane season,” Bell said. “Even people who live inland should be prepared for severe weather and flooding from a tropical storm or a hurricane.” |
