Hurricane Irene

Hurricane Irene

Hurricane Irene

 

Hurricane Irene is an active tropical cyclone that currently poses a threat to the Greater Antilles. The ninth named storm of the season, Irene developed from a well-defined Atlantic tropical wave, which showed signs of tropical development east of the Lesser Antilles. It developed a stable amount of atmospheric convection and a closed cyclonic circulation center, prompting the National Hurricane Center to initiate public advisories on late on August 20. Subsequent convective organization occurred as it passed the Leeward Islands, and by August 21 it moved very close near Saint Croix.

On August 15, 2011, a tropical wave exited the African coast dropping into the Atlantic, characterized by distinct low-level cyclonic rotation and deep tropical moisture.[1] It remained well-defined while moving steadily westward for several days through the Cape Verde Islands, although at the time any notable convection occurred well to the southwest of its axis.[2] As the wave distanced itself from the islands, development of thunderstorms and showers in its proximity continued to remain scarce, and it became rather broad in appearance.[3] On August 19, the convective structure began to show signs of organization as the associated atmospheric pressure lowered, and with a progressively favorable environment situated ahead of the wave its chances of undergoing tropical cyclogenesis markedly increased.[4][5] The strong thunderstorm activity continued to become more pronounced around the main low-pressure feature; by August 20, the National Hurricane Center (NHC) noted that tropical cyclone formation was imminent as the wave neared the Lesser Antilles.[6] A reconnaissance aircraft confirmed the presence of a small surface circulation center just southwest of a burst of vigorous convection and unusually high sustained winds, which indicated sufficient organization for the low to be upgraded into Tropical Storm Irene at 2300 UTC that day.

Upon being classified, Irene was positioned about 190 mi (305 km) east of Dominica along weakening high pressure over the west-central Atlantic, inducing a roughly west-northwestward path for most of its journey through the eastern Caribbean.[7] Its mid-level circulation continued to become better established as hints of pronounced banding features curved north of the surface center.[8] On August 21, the surface center reformed closer to the deepest convection; furthermore, an anticyclone aloft provided supportive outflow over the cyclone. With the improved structure, as well as light wind shear and high sea surface temperatures, Irene was forecast to strengthen to near hurricane force prior to landfall in Hispaniola.[9][10] Over the subsequent day, Irene traced more northward than initially expected—all the while passing very near the island of Saint Croix[11]—toward Puerto Rico, where it underwent a considerable increase in wind circulation velocities to near hurricane strength and deepening convection.[12]