Tropical Storm Ernesto

Pre-Landfall 1 | Summary
Posting Date: August 3, 2012, 10:00:00 AM

Tropical Storm Ernesto is the fifth named storm in the Atlantic this year and the first to originate in the tropics. It was classified as a tropical storm one day later than last year’s “E” storm. Ernesto was upgraded from a tropical depression to a tropical storm last night by the National Hurricane Center (NHC) after a Hurricane Hunter plane discovered surface winds of tropical storm strength. The storm brushed Barbados this morning, then passed between St. Lucia and St. Vincent around 7AM EDT.

Current Conditions

Ernesto currently has 50 mph maximum sustained winds with a reported wind gust of 63 mph in St. Lucia and 43 mph sustained winds in Barbados. Up to 5 inches of rain is expected in the Windward Islands through today. Barbados closed its Grantley Adams International Airport at midnight last night, with an expected re-opening time of 10AM EDT today. The regional carrier LIAT canceled a dozen flights scheduled to fly among many of the Windward Islands. St. Vincent closed its E.T. Joshua International Airport at 11PM last night, with a possible re-opening at 4PM today. Schools and shops on St. Lucia were closed today and not expected to re-open before noon.

Exposure at Risk

On the islands affected by winds from Ernesto, most residential buildings are of masonry or wood construction type. Building codes are adopted in these countries, but the enforcement tends to be low. Most insurable residential properties in Barbados have concrete-block masonry walls and timber-framed roof structures with metal sheets, asphalt shingles, or “Spanish” tile cover. Concrete block construction is also common in St. Lucia and St. Vincent, with sheet metal being the prevalent material for residential roof cover. At the level of wind speed observed, very minor damage may be seen to exterior cladding and roofing, but both reinforced masonry and concrete block construction should perform well. Commercial buildings in these areas typically consist of reinforced masonry, concrete, and steel, which would be largely unaffected at this wind speed. Light metal commercial structures, however, may have some minor damage. Non-engineered buildings can be vulnerable to damage from flooding, though precipitation levels have been low due to the low intensity and fast forward speed of the storm.

Forecast and Intensity

Ernesto is moving westward at a relatively fast clip of 21 mph, which is notable given its low latitude. Its high speed can be attributed to a strong ridge of high pressure to the north of the storm, which is also keeping Ernesto moving westward, instead of curving northward. The high forward speed enhances the asymmetry of the storm; nearly all of the tropical storm force winds are on the right (north) side of Ernesto. As this system continues on a generally westward path from the Atlantic into the Caribbean Sea, it will encounter a bit less wind shear (shear prevents systems from organizing and intensifying), though wind shear will still be too high to allow extreme intensification. On the other hand, Ernesto will pass over warm sea-surface temperatures that are conducive to better organization and development into a hurricane. On Monday morning, Ernesto is forecast to pass south of Jamaica as a Category 1 hurricane, and then pass south of the Cayman Islands that afternoon. Beyond three days out, the forecast is much less certain. Some models show Ernesto entering the Gulf of Mexico and making a U.S. landfall, while others show a landfall in Mexico or Central America. AIR’s Caribbean Tropical Cyclone team will be monitoring Ernesto closely during the next few days. The team is also watching two other systems: a robust tropical wave that just exited Africa, which the NHC is calling “Invest 90L” and is already giving a 30% chance of developing into a depression in the next two days; and an area of low pressure over the Bahamas, which the NHC has assigned a 10% chance of developing in the next two days.

Pre-Landfall 1 | Downloads
Posting Date: August 3, 2012, 10:00:00 AM