Variety of Factors Contributed to Average Hurricane Season in 2007, Csu Forecast Team Says

Note to Editors: The complete 2007 season verification report is available with the press release at Forecast verification totals, the complete 2007 season verification report, as well as related research, detailed descriptions of forecast factors, previous forecasts and explanations of individual storms, will be available no later than 8:30 a.m. MST at

Cooler water and wind shear in the central tropical Atlantic resulted in this season not being above average as predicted by the Colorado State University hurricane forecast team.

An extensive write-up of the full characteristics of the Atlantic basin 2007 season is available at

A total of 14 named storms, six hurricanes and two major hurricanes developed in 2007 – an average season when compared with the 1950-2000 average. The CSU hurricane forecast team had predicted 17 named storms, nine hurricanes and five major hurricanes with their April and June forecasts; they later lowered it to 15 named storms, eight hurricanes and four major hurricanes with their August update.

The team has over-predicted the hurricane activity of the past two seasons. In seven of the past nine years, the team correctly predicted above- or below-average activity with its seasonal hurricane forecasts from their early August forecast.

"The reasons for this year’s average season are challenging to explain," said Phil Klotzbach, lead author on the forecasts. "It is impossible to understand how all these processes interact with each other to 100 percent certainty. Continued research should help us better understand these complicated atmospheric/oceanic interactions."

The newest report summarizes tropical cyclone activity in the Atlantic basin during the 2007 hurricane season and compares the team’s seasonal and monthly forecasts to what actually occurred.

"The 2006 and 2007 Atlantic basin hurricane seasons were much less active than 2004 and 2005," said Gray, who led the forecast team at Colorado State for 23 years. "Overall, the season witnessed average activity."

The Colorado State team made its first long-range seasonal forecast, which called for an above-average hurricane season, on Dec. 8, 2006, and then issued seasonal updates on April 3, May 31, Aug. 3, Sept. 4 and Oct. 2.  All of these forecast updates also predicted above-average activity.  

The 2006 and 2007 hurricane seasons contrasted sharply with 2004 and 2005.

Gray and his Colorado State team have provided seasonal Atlantic basin hurricane forecasts for 24 years. Until Gray began developing his forecast model in the early 1980s, there were no objective methods for predicting whether forthcoming hurricane seasons were likely to be active, inactive or near average.

In 2004, the Colorado State team helped create the Landfalling Hurricane Probability Web page – at – that includes specific forecasts of the probability of landfalling tropical storms and hurricanes of category 1-2 and 3-4-5 intensity for 11 regions and 55 subregions along the U.S. Gulf and East Coast. These subregions are further subdivided into 205 coastal and near-coastal counties.

"We’re always working to improve our forecasting skills, and we hope these forecasts will continue to be of assistance to coastal populations, emergency managers, insurance providers and others concerned about Atlantic basin hurricane activity," Klotzbach said.

Gray and his team plan to issue the first seasonal forecast of the 2008 Atlantic basin hurricane season on Dec. 7.