Just days after the 2006 hurricane season officially -- and quietly -- ended (see Daily GPI, Dec. 1), a respected London-based forecaster on Thursday issued a much stormier outlook for 2007, predicting that 16 tropical storms are likely to occur in the Atlantic basin next season, including nine hurricanes and four so-called "intense," or Category 3-5 storms.
Of the total number of storms forecast for the Atlantic basin, five likely will strike land in the United States, according to the Tropical Storm Risk (TSR). The TSR, compiled by Benfield University College London's Hazard Research Centre, said "current and projected climate signals" indicate Atlantic basin and U.S. landfalling tropical cyclone activity is forecast to be 50% greater than the 1950-2006 norm in 2007. The forecast spans the period June 1-Nov. 30, 2007, and employed data through the end of last month.
"There is a high (80%) likelihood that activity will be in the top one-third of years historically," wrote forecasters Mark Saunders and Adam Lea.
Using TSR's Accumulated Cyclone Energy (ACE) Index, the forecast is based on two predictors: the forecasted July-September 2007 trade winds, which are expected to be weaker-than-normal, and the predicted sea surface temperatures forecast for August-September 2007, which are predicted to be warmer. Stronger trade winds usually dissipate storms more quickly, while warmer waters help storms to form and build.
"At present, TSR anticipates both predictors having a moderate enhancing effect on activity."
Next year, TSR is forecasting that four (3.9, plus or minus 1.8) storms in the Atlantic basin will reach a wind speed of at least 93 knots, which would be Category 3-5 hurricanes. TSR also is forecasting almost nine Category 1-5 storms (8.8, plus or minus 2.9) will reach a wind speed at least 63 knots. It also predicts about 16 tropical storms (15.7, plus or minus 4.6) will reach wind speeds of at least 33 knots.
Comparatively, the 57-year climate norm between 1950 and 2006 forecast averaged about three intense hurricanes (2.7, plus or minus 1.9), about six hurricanes (6.2, plus or minus 2.6) and 10.3 tropical storms (plus or minus 4).
The TSR said an unusual mix of conditions led to fewer storms than originally forecast this past hurricane season.
"The below-average 2006 hurricane season was due to the presence of considerable African dry air and Saharan dust during August and September, which inhibited thunderstorm occurrence and therefore tropical storm development, and to the unexpected onset of El Nino conditions from mid-September," noted the TSR forecasters. "There is no precedent for these factors together having been so influential before."
For more on the long-range forecast, visit http://tropicalstormrisk.com .The first TSR monthly forecast update is scheduled for Jan. 5.
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