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Hurricane Irene : strengthens to category 2 and moves towards the South-Eastern Bahamas

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Just before 8pm last night, Hurricane Irene achieved Category 2 strength, buoyed by low wind shear and warm sea surface temperatures. According to the National Hurricane Center’s (NHC) 11 a.m. EDT advisory today, Irene is 70 miles south of the popular cruise destination, Grand Turk Island. Maximum sustained winds are 100 miles per hour. In addition to strengthening last night, the storm track shifted slightly east, which will keep Irene over open water longer as it tracks north this week, possibly allowing it to undergo more significant intensification than had previously been forecast. 

 “Today, Irene is expected to track offshore of the northern coast of the Dominican Republic and Haiti, where tropical storm conditions will continue to be felt for the next several hours,” said Scott Stransky, scientist at AIR Worldwide. “Four to 8 inches of rain are possible. Irene will approach the Turks and Caicos Islands and the Southeastern Bahamas tonight.”

Stransky continued, “Currently, Irene’s hurricane-force winds currently extend outward about 50 miles, while its tropical storm-force winds extend up to 205 miles. The storm has a much more symmetrical wind footprint than it had yesterday. Given its forecast track, damaging winds will be impacting the Turks and Caicos Islands and Southern Bahamas throughout the day today.  Already, tropical storm conditions are spreading over these regions, which could receive 5 to 10 inches of rainfall and may experience storm surge up to 13 feet. In the Central Bahamas, to the north, tropical storm conditions from Irene are forecast to impact land as early as late tonight, with hurricane conditions expected there by tomorrow morning. By Thursday, when the storm may reach Category 4 strength, it will be impacting the northern Bahamas, including the three largest cities: Nassau, Freeport, and Marsh Harbour.”

A hurricane warning is now in place for the Turks and Caicos Islands, as well as entire Bahamas. Meanwhile, the hurricane warning that had been in effect for the north coast of the Dominican Republic this morning has been downgraded to a tropical storm warning. A tropical storm warning is also in effect along Haiti’s north coast.

Irene is the Atlantic basin’s first hurricane of the 2011 season; it achieved this status yesterday morning (Monday, August 22) when its winds strengthened to 75 miles per hour as it exited Puerto Rico’s northern coast. Strong winds and heavy rain from Irene disrupted electricity to 800,000 people in Puerto Rico. In total, Irene has cut power to more than a million people on the island. The storm also dumped 10 inches of rain in Naguabo and seven inches in the island municipality of Vieques. These heavy rains caused several rivers to burst their banks and many trees and power lines to fall across roadways.

 “After impacting Puerto Rico yesterday, Irene continued west-northwest toward the Dominican Republic and Haiti,” commented Stransky. “Because most of Irene’s winds were to the north of the storm at the time, however, the Dominican Republic and Haiti were spared the worst winds yesterday, meaning the most significant damage on the island of Hispaniola has been from precipitation. Today, tropical storm conditions will continue in this region; Irene could produce rainfall amounts of 4 to 8 inches in northern Hispaniola, with isolated maximum amounts of up to 15 inches possible in the mountains. This heavy rain could lead to flash floods and mud slides.”

According to AIR, Irene’s strong winds and forecast track could result in significant damage in the Bahamas, although Nassau, with its concentration of exposure, is currently expected to be on the left-hand, weaker side of the storm. As always, however, it is important to note that there is considerable uncertainty with respect to Irene’s future track.

Both in the Turks and Caicos Islands and in the southern islands of Bahamas, the dominant residential construction types are reinforced and unreinforced masonry. According to AIR, unreinforced masonry may sustain moderate damage from a Category 2 hurricane, but damage to reinforced masonry structures should be limited to roofs and openings. Commercial structures in these regions are commonly made of reinforced masonry and reinforced concrete; these construction types should not sustain significant damage from storms of Category 2 strength, as Irene is now. Meanwhile, light metal buildings, which are common in small and large industrial facilities in these regions, may sustain significant damage. Building code enforcement in the Bahamas is relatively high.

According to AIR, in the Turks and Caicos islands, insured commercial, residential (and auto exposure) is estimated to be USD 3.1 billion (in 2009 dollars). In the southernmost Bahamas islands—Inagua, Mayaguana and Crooked Island—insured exposure (in 2009 dollars) is USD 218 million. However, these islands are relatively unpopulated, accounting for less than 0.50% of the total Bahamas population, as of 2010. It should be noted that over the next few days, Irene will be moving into much more populated areas.

Stransky continued, “Again, there is considerable uncertainty in the forecast path for Irene later this week. Current forecasts place the storm on a track that could bypass Florida and make landfall in North Carolina on Saturday. Some forecast tracks show Irene impacting the Northeast coast after that, while others keep Irene off the coast entirely, and out over open water. The last hurricane to make landfall in the U.S. was Ike, a Category 2 storm that had maximum winds of 95 mph and struck Texas and Louisiana in 2008.”

Hurricane Irene is the ninth named storm of the 2011 Atlantic hurricane season and the first hurricane. AIR continues to monitor Hurricane Irene closely and will provide updates as warranted. (Additional information about losses will be made available after the storm has finished impacting all the Caribbean islands, which—on the NHC’s current track—will be by Friday morning EDT.)

Source : AIR Worldwide