ImpactWeather is forecasting a less active hurricane season in 2009, as compared to the 2008 season, however we think that there may be an elevated risk of an impact across the southeast U.S. this season. The primary threat region will be located along the eastern Gulf coast and up the Atlantic Seaboard, especially from Florida to the Carolinas
For 2009, we’re forecasting a total of 12 named storms, 7 of which will become hurricanes and 3 of those hurricanes major hurricanes on the Saffir-Simpson scale. However, ImpactWeather has developed a new hurricane scale that takes into account both a hurricane’s maximum sustained winds as well as the size of its wind field. We call this new 50-point scale the Hurricane Severity Index, or HSI for short. On our scale, Ike had a total of 27 points at landfall, while Gustav made landfall with a total of 20 points out of a possible 50. This season, we are forecasting that 4 hurricanes may reach a total of 20 points on the HSI. Of those 4 hurricanes, 2 may reach an HSI value of 20-25 points, one may reach an HSI value of 26-30 points and one may reach an HSI of greater than 30 points.
We think that at least half of all of the 2009 storms will remain in the open Atlantic, considering the Azores-Bermuda high is expected to be weaker. This would allow for less wind shear across the Atlantic Basin and a better chance for developing storms to re-curve safely out to sea. We are also putting a higher number of storms in the Caribbean due to above normal water temperatures just to the east of the Caribbean. Over the Gulf of Mexico, we are predicting 3 named storms. By far, the area of most concern will be over the Florida Peninsula where 75% of the identified storms made landfall in previous analogous seasons. After Florida, there is a much smaller secondary maximum threat over the Texas Coast and eastern Mexican Coast from Matamoros to Veracruz.
Current sea surface temperature anomalies still indicate above-normal water temperatures throughout much of the Atlantic Basin. Warmer than normal water typically correlates to more tropical cyclones. In addition, there is a possibility of a weak El Niño developing over the Pacific Ocean this summer. El Niño represents warmer than normal water (0.5C or more) over the eastern Tropical Pacific, which typically correlates to increased wind shear and less tropical activity over the Atlantic Basin. We think there is a chance (40%) a weak El Niño will develop by the start of hurricane season, but we think there is a greater chance (60%) the El Niño will be delayed until late summer / early fall due to cold water over the eastern Pacific moving southward into the eastern Tropical Pacific.
