Isaac Poses Significant Storm Surge Threat to Southern Gulf States
27-Aug-12
Tropical Storm Isaac is currently in the eastern Gulf of Mexico approximately 200 miles west of Florida headed towards New Orleans, Louisiana. Isaac is expected to intensify to hurricane status in the next 24 hours with a 50% probability that it will remain at hurricane intensity until the expected landfall late Tuesday, August 28 (if Isaac does make landfall as a hurricane, it is likely to be an Category 1 or weak Category 2 hurricane). The center of Isaac is large and poorly formed, and the combination of large storm size, slow forward motion, and the bathymetry of this portion of the coast is producing an expectation for a large storm surge (6 to 12 feet of storm surge in locations). In the northern Gulf of Mexico, wave heights are predicted to be up to 30 feet in places north of latitude 27N, presenting a limited potential for damage to fixed and floating assets in the Gulf.
Wednesday, August 29 marks the region’s seventh anniversary of Hurricane Katrina’s landfall in 2005. Isaac is following a very similar path and is a broad storm with tropical storm force winds extending out up to 205 miles (Katrina had tropical storm force winds extending up to 230 miles). In the wake of Hurricane Katrina, the US Army Corps of Engineers constructed the Hurricane and Storm Damage Risk Reduction System (HSDRRS), a perimeter defense against 100-year storms in the New Orleans area. This defense system is expected to hold back surge from Isaac in the New Orleans region.
Over the weekend, Isaac stayed offshore of western Florida and winds in Florida stayed well below hurricane strength (tropical storm force gusts were felt Sunday along much of the coast of southeast Florida, from West Palm Beach through the Keys). Storm surge and rainfall in Florida remain well below the severity from Hurricanes Charley (August 2004) and Ivan (September 2004). Isaac made landfall in southwestern Haiti early Saturday, August 25, with maximum sustained winds of 70 mph and heavy rainfall amounts of up to 20 inches. Isaac caused numerous destructive flash floods and mud slides before emerging from Haiti into the Windward Passage with its maximum winds down to 60 mph. The center briefly crossed the eastern tip of Cuba around midday Saturday.
Tropical Storm Isaac Potential Storm Track - August 27, 2012
Source: National Hurricane Center (NHC)
At 10 am CDT, Monday, August 27, the center of Isaac was located at latitude 26.1N, longitude 85.3W, and was 310 miles southeast of the mouth of the Mississippi River. Maximum winds were 65 mph, and some strengthening is forecast. Isaac is expected to become a hurricane before reaching the northern Gulf Coast late Tuesday.
Isaac is moving to the northwest at 14 mph, and this motion is expected to continue over the next day or so, with a gradual decrease in forward motion. The current forecast track has the center of Isaac reaching the mouth of the Mississippi River late afternoon on Tuesday, August 28, and in the vicinity of New Orleans Wednesday morning.
A hurricane warning is in effect for the northern Gulf Coast from east of Morgan City, Louisiana, through Destin, on the Florida panhandle, including metropolitan New Orleans.
With Isaac expected to slow its forward motion as it approaches the northern Gulf Coast, rainfall amounts are predicted to be high, with 6 to 12 inches, and maximum amounts of 18 inches possible in southeastern Louisiana, Mississippi, southern Alabama, and the western Florida panhandle. Current river conditions lead to an expectation of localized flooding but minimal widespread disruption.
Because of its broad size, Isaac poses a significant storm surge threat to the northern Gulf Coast. Should it occur during the time of high tide, a surge of 6 to 12 feet is possible in southeastern Louisiana, Mississippi, and Alabama.
EQECAT will continue to monitor this event and provide updates as more information becomes available.
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