UPDATE: TS Ernesto Crossing Caribbean; AIR Analysis

August 6, 2012

Tropical Storm Ernesto is continuing along the track forecast by the National Hurricane Center in Miami, as it crosses the southern Caribbean, heading towards Mexico’s Yucatan Peninsula.

The most recent NHC bulletin said maximum sustained winds were 50 mph, 85 km/h, with higher gusts. “Some strengthening is forecast as Ernesto moves over the northwestern Caribbean sea on Monday and Tuesday. Tropical storm force winds extend outward up to 125 miles…205 km from the center.

“Tropical storm conditions are expected in Jamaica overnight tonight and early Monday morning. Tropical storm conditions are possible in Grand Cayman overnight tonight and early Monday and in the watch area along the coast of Honduras by late Monday.”

Catastrophe modeling firm AIR Worldwide has issued a bulletin analyzing the threat posed to land by Ernesto. AIR explained that 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.”

Scott Stransky, senior scientist at AIR Worldwide, noted: “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.”

Sources: National Hurricane Center and AIR Worldwide

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