Hanna Succumbs to Wind Shear in Atlantic

According to catastrophe risk modeling firm AIR Worldwide, storm development in the tropical Atlantic was even more active on Tuesday than it was on Monday.

Shortly after Gustav came ashore in Louisiana, Hanna began battering the southeastern Bahamas with hurricane force winds. Shortly thereafter, Tropical Storm Ike was named. On Tuesday morning, forecasters at the National Hurricane Center began tracking a tropical depression off the coast of Africa. Now upgraded to tropical storm Josephine, it is the 10th named storm of the season. Josephine's sustained winds are near 40 mph and further strengthening is forecast.

“Hanna, which was upgraded from a tropical storm to a hurricane on Monday afternoon, succumbed to significant vertical wind shear on Tuesday morning and was downgraded again to a tropical storm,” said Dr. Peter Dailey, director of atmospheric science at AIR Worldwide. “As of 8:00 p.m. EDT on Tuesday, Hanna is located southeast of Great Inagua Island in the southeastern Bahamas and about 450 miles southeast of Nassau. Maximum sustained winds are near 65 mph.”

“Hanna had successfully fought off wind shear on Monday to become the fourth hurricane of the 2008 season. The storm then stalled over the sparsely populated southeastern Bahamas, held in place by a large area of high pressure extending from the Great Lakes southward. Hanna's slow and meandering motion is expected to continue for the next 24 to 36 hours before a subtropical ridge over the west-central Atlantic is forecast to turn the storm to the northwest.”

“At present, Hanna is dumping heavy rain on the southeastern Bahamas, the Turks and Caicos Islands, and Haiti, which was already saturated by rain from Gustav last week. Accumulations of 4 to 8 inches are expected, with isolated amounts up to 12 inches.”

However, the dynamical forecast models are in reasonably good agreement that by Wednesday Hanna will speed up and eventually make a U.S. landfall somewhere between Savannah, Georgia and Myrtle Beach, South Carolina.

Until then, there is considerable uncertainty with respect to Hanna's track through the Bahamas. The NHC's most likely track has Hanna skirting the Bahamas to the north and well away from the most heavily populated islands of New Providence (and the capital Nassau) and Grand Bahama. Other models show a more southernly track directly through the middle of the islands. Given that the moderate wind shear that Hanna is currently experiencing is expected to diminish today—making some additional intensification likely—AIR is closely monitoring this storm and will provide updates as warranted by events.

Meanwhile, Gustav—now a tropical depression centered over northwest Louisiana—continues to drop heavy rain over portions of Texas, Louisiana, and Arkansas. However, local officials are relieved that apart from some overtopping of the Industrial Canal in New Orleans' Lower Ninth Ward, the city's floodwalls seem to have survived largely, if not entirely, intact.