In an early assessment Tropical Storm Risk (TSR) forecast “a return to high hurricane activity in 2007.” The London-based consortium of experts on insurance, risk management and seasonal climate forecasting led by the Benfield UCL Hazard Research Centre at University College London warned that the below-average 2006 hurricane season probably won’t be repeated. “Atlantic basin and U.S. landfalling hurricane activity will be 60 percent above the 1950-2006 norm next season,” according to TSR.
TSR more or less accurately predicted the intense hurricane activity in 2004-05, but, along with all of the other forecasters, its predictions for 2006 didn’t materialize – to the great relief of Florida and Gulf Coast residents, as well as the insurance industry. However, TSR indicated that “it is 76 percent likely that U.S. landfalling hurricane activity in 2007 will be in the top one-third of years historically.”
TSR’s long-range hurricane prediction is summarized as follows:
— A 79 percent probability of an above-normal Atlantic hurricane season, a 15 percent probability of a near-normal season and only a 6 percent chance of a below-normal season.
–16 tropical storms for the Atlantic basin as a whole, with nine of these being hurricanes and four intense hurricanes.
–A 76 percent probability of above-normal U.S. landfalling hurricane activity, a 15 percent likelihood of a near-normal season and only a 9 percent chance of a below-normal season.
–Five tropical storm strikes on the U.S., of which two will be hurricanes.
–Two tropical storm strikes on the Caribbean Lesser Antilles, of which one will be a hurricane.
TSR said the “the two main climate factors influencing the hurricane forecast for 2007 are the expected values in August and September for the speed of trade winds which blow westward across the tropical Atlantic and Caribbean Sea and the temperature of the sea waters between west Africa and the Caribbean where many hurricanes develop.
“The former influences cyclonic vorticity (the spinning up of storms) while the latter provides heat and moisture to power incipient storms. TSR anticipates weaker than normal trades and warmer than normal waters in 2007: conditions which both favor an above-average hurricane season.”
Professor Mark Saunders, TSR’s lead scientist, noted: “In addition to our core model prediction, further support that 2007 will see above normal hurricane activity to 80 percent likelihood comes from the link between El Niño events in +ve AMO (Atlantic Multidecadal Oscillation) years – as we are currently experiencing – and the level of hurricane activity in the following year. Since 1950 there have been 10 El Niño events in +ve AMO years. Eight out of ten of these (i.e. 80 percent of years) were followed by above-normal hurricane activity next season. This result occurs because El Niño conditions tend to reverse sign by the following summer.”
Saunders defended the forecasters recent performance by indicating that “the 2006 hurricane season is atypical of years since 1950 and should not reflect badly on the general capability of forecasts. 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 Niño conditions from mid-September. There is no precedent for these factors together having been so influential before.”
TSR forecasts may be accessed through the web site: www.tropicalstormrisk.com.
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