Colorado State University Team Predicts Fewer Hurricanes Will Make Landfall

May 31, 2006

The U.S. Atlantic basin is likely to experience another active hurricane season, but coastal regions may face fewer land-falling major hurricanes than last year, according to Prof. William Gray and the Colorado State University forecast team. The team maintained its earlier predictions for the 2006 hurricane season, which starts June 1.

Colorado State’s forecast for the 2006 hurricane season anticipates 17 named storms forming in the Atlantic basin between June 1 and Nov. 30. Nine of the 17 storms are predicted to become hurricanes, and of those nine, five are expected to develop into intense or major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.

The 2005 season witnessed 27 named storms, 15 hurricanes and seven intense hurricanes. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

“The Atlantic Ocean remains anomalously warm and neutral ENSO (El Nio – Southern Oscillation) conditions are observed in the tropical Pacific,” Phil Klotzbach, a member of the Colorado State University hurricane forecast team and lead author on the forecast, explained. “We expect neutral ENSO conditions to be present during the upcoming hurricane season. When the tropical Atlantic is warm and neutral ENSO conditions are present, Atlantic basin hurricane activity is usually enhanced.”

The hurricane forecast team predicts tropical cyclone activity in 2006 will be 195 percent of the average season. By comparison, 2005 witnessed tropical cyclone activity that was about 275 percent of the average season.

“If the atmosphere and the ocean behave as they have in the past, we should have a very active season, but that doesn’t necessarily translate into storms that produce as much destruction as last year,” explained Gray.

The current active period of Atlantic major hurricane activity is expected to continue for another 15 to 20 years. Still, Gray said, it is statistically unlikely that the coming 2006-2007 hurricane seasons, or those that follow, will have the number of major hurricane U.S. landfall events as occurred in 2004-2005.

The hurricane forecast team’s probabilities for a major hurricane making landfall on U.S. soil are as follows:

– An 82 percent chance that at least one major hurricane will make landfall on the U.S. coastline in 2006 (the long-term average probability is 52 percent).

– A 69 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 38 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).

The team also predicted above-average major hurricane landfall risk in the Caribbean.

The forecast team’s landfall probabilities for the United States are based upon total predicted Net Tropical Cyclone activity, which is an aggregate measure of activity expected during the season and new mid-level steering flow predictors that show moderate skill in predicting whether storms are more likely to make landfall along the Gulf Coast, the Florida Peninsula and East Coast, or stay out to sea without making landfall. This year’s steering current predictors indicate that the Florida Peninsula and East Coast have an especially heightened risk of experiencing landfalling hurricanes.

“In any one season, most U.S. coastal areas will not feel the effects of a hurricane no matter how active a season,” Klotzbach said. “The probability of landfall for any one location along the coast is very low. However, low landfall probability does not ensure that hurricanes will not come ashore, so coastal residents should always be prepared.”

The 2004-2005 season was unusually destructive because of favorable broad-scale Atlantic upper-air steering currents that caused so many hurricanes to come ashore, Gray said.

Probabilities of tropical storm-force, hurricane-force and intense 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 Landfall Probability Web site. The site provides U.S. landfall probabilities for 11 regions, 55 sub-regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. The Web site, available to the public at, is the first publicly accessible Internet tool that adjusts landfall probabilities for regions, sub-regions 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.

The hurricane team’s forecasts are based on the premise that global oceanic and atmospheric conditions, such as El NiƱo, sea surface temperatures and sea level pressure, that preceded active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons.

For 2006, Gray and the hurricane forecast team expect continued warm tropical and north Atlantic sea-surface temperatures, prevalent in most years since 1995, as well as neutral ENSO conditions, a recipe for enhanced Atlantic basin hurricane activity. These factors are similar to conditions that occurred during the 1961, 1996, 2001 and 2004 seasons. The average of these four seasons had well above-average activity, and Klotzbach and Gray predict the 2006 season will have comparable activity to the average of these four years.

Gray does not attribute changes in Atlantic hurricane activity to global warming.

“Nature is causing these things, it’s not human-induced global warming,” Gray said. “Seasonal and monthly variations of sea surface temperature within individual storm basins show low correlations with monthly, seasonal and yearly variations of hurricane activity.”

Klotzbach is the lead author on the team’s seasonal, monthly and landfall probability forecasts. Gray has been at the helm for 22 years; he joined Colorado State University in 1961.

Source: Colorado State University

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