London-based Tropical Storm Risk (TSR) is forecasting 2007 Atlantic basin and U.S. landfalling tropical cyclone activity will be about 75% above the 1950-2006 norm, the highest March forecast for activity in any year since the forecaster began issuing real-time forecasts in 1984. Based on current and projected climate signals, TSR said there is a "high probability" for an active hurricane season.

The March forecast update for the 2007 season, which runs June 1 to Nov. 30, used data compiled through the end of February. TSR found an 86% "likelihood" that the Atlantic hurricane season would be above normal, or in the top one-third of years historically. The forecaster is estimating an 11% chance this season will be near normal, and only a 3% chance it will be below normal.

In December, TSR predicted 16 tropical storms were likely to occur in the Atlantic basin this season, including nine hurricanes and four so-called "intense," or Category 3-5 storms (see Daily GPI, Dec. 8, 2006). Five of the storms were forecast to likely strike land in the United States.

TSR now is forecasting 17 tropical storms will form, which still includes nine hurricanes and four Category 3-5 storms. Five storms, including two hurricanes, are expected to make U.S. landfall, the TSR estimated.

TSR said its two "predictors" are the forecasted July-Sept. 2007 trade wind speed over the Caribbean and tropical North Atlantic, and the estimated August-September 2007 sea surface temperature in the tropical North Atlantic. The trade winds influence cyclonic vorticity (spinning up of storms) in the main hurricane track region, while warm temperatures provide heat and moisture to power storms in the region.

"At present, TSR anticipates both predictors having a moderate enhancing effect on activity," said Mark Saunders and Adam Lea, who track data for TSR through the Benfield University College London Hazard Research Centre in the United Kingdom. "The El Nino conditions present since September 2006 dissipated rapidly during February. The sudden El Nino dissipation is the main reason for the TSR forecast for hurricane activity in 2007 rising."

TSR will issue its next update in April. For more information on TSR, click here.

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