Colorado State University Hurricane Forecast Team Predicts Above-Average Atlantic Basin Hurricane Season in 2008

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Colorado State University hurricane forecasters today maintained an earlier forecast that called for a very active 2008 season. The hurricane forecast team is calling for 15 named storms forming in the Atlantic basin during this year’s hurricane season. Eight of the storms are expected to become hurricanes with four becoming intense hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.

Tropical Storm Arthur, which formed on May 31, is included in the CSU hurricane forecast, meaning that 14 more named storms are expected this year.

"Conditions in the tropical Atlantic look quite favorable for an active hurricane season. Sea surface temperatures are anomalously warm, while sea level pressures and levels of vertical wind shear are quite low," said Phil Klotzbach of the Colorado State hurricane forecast team and the lead author of the forecast. "Our primary concern is the warming waters in the equatorial Pacific. At this point, we do not believe that an El Nino will develop by late this summer; however, this is a possibility that must be monitored closely."

The hurricane forecast team is using a new statistical model to predict tropical cyclone activity this year. This model shows considerable improvement in skill over the models that have been used to issue June predictions over the past few years.

The hurricane forecast team predicts tropical cyclone activity in 2008 will be 160 percent of the average season. By comparison, 2005 witnessed tropical cyclone activity that was about 275 percent of the average season. The 2007 season witnessed tropical cyclone activity that was approximately 100 percent of the average season with a total of 15 named storms, six hurricanes and two major hurricanes forming last year. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

The hurricane forecast team reiterated its probabilities for a major hurricane making landfall on U.S. soil:

– A 69 percent chance that at least one major hurricane will make landfall on the U.S. coastline in 2008 (the long-term average probability is 52 percent).

– A 45 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 44 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 Atlantic has seen a very large increase in major hurricanes during the 13-year period of 1995-2007 (average 3.8 per year) in comparison to the prior 25-year period of 1970-1994 (average 1.5 per year)," said William Gray, who began forecasting hurricane seasons at Colorado State 25 years ago. "This large increase in Atlantic major hurricanes is primarily a result of the multi-decadal increase in the Atlantic Ocean thermohaline circulation (THC) that is not directly related to global temperature increase. Changes in ocean salinity are believed to be the driving mechanism."

For 2008, Klotzbach and Gray 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 1951, 1961, 2000 and 2001 seasons. The average of these four seasons had well above-average activity, and Klotzbach and Gray predict the 2008 season will have activity in line with the average of these four years.

"This active cycle is expected to continue for another decade or two at which time we should enter a quieter Atlantic major hurricane period like we experienced during the quarter-century periods of 1970-1994 and 1901-1925," Gray said. "Atlantic hurricanes go through multi-decadal cycles."

The past two years – 2006 and 2007 – had slightly below-average and average activity, respectively, with only one Category 1 hurricane (Humberto) making landfall on U.S. soil in 2007. The Colorado State hurricane forecast team has said the hurricane seasons of 2004 and 2005 were anomalies: Florida and the Gulf Coast were ravaged by four landfalling hurricanes each year. Hurricanes Charley, Frances, Ivan and Jeanne caused devastating damage in 2004 followed by Dennis, Katrina, Rita and Wilma in 2005.

"Coastal residents need to prepare for every hurricane season, regardless of seasonal predictions," Klotzbach said. "There is inherent uncertainty in seasonal predictions. Also, seasonal forecasts cannot say anything about when or where storms are going to make landfall."

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 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. The Web site, available to the public at, is the first publicly accessible Internet tool that adjusts landfall probabilities for 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 website has recently been upgraded to provide increased functionality.

The hurricane team’s 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 provide meaningful information about similar trends in future seasons.

The team will issue seasonal updates of its 2008 Atlantic basin hurricane activity forecast on Aug. 5, Sept. 2 and Oct. 1. These forecasts will contain predictions for the individual months of August, September and October.



-Released June 3, 2008-

Tropical Cyclone Parameters

(1950-2000 Climatological Averages in parentheses) Forecast for 2008

Named Storms (9.6)* 15

Named Storm Days (49.1) 80

Hurricanes (5.9) 8

Hurricane Days (24.5) 40

Intense Hurricanes (2.3) 4

Intense Hurricane Days (5.0) 9

Net Tropical Cyclone

Activity (100%) 160

* Numbers in ( ) represent average year totals based on 1950-2000 data.