August 29th, 2012

Update: Hurricane Isaac

Posted at 1:49 PM ET

isaac-3-smallHurricane Isaac made a second landfall near the mouth of the Mississippi River, at Port Fourchon, Louisiana early this morning, exactly seven years following the landfall of Katrina. The storm center is presently about 45 miles Southwest of New Orleans. Isaac is a large and slow-moving storm, with potential hazards as far away as east Texas and west Florida. Hurricane conditions can be expected to continue for warned areas into this afternoon.

Isaac is moving inland over the state of Louisiana, at an excruciatingly slow speed of 6 mph. Near hurricane force winds have been reported at New Orleans Airport in Kenner, Louisiana. Storm surge levels of 8 feet are still reported at certain marine stations, after a peak of 11 feet; surge levels on Lake Pontchartrain have been reported as high as 5 feet. Inland flooding continues to be a significant threat due to the slow motion of the storm, and the flat terrain of the affected areas. Inland tornadoes will also be an ongoing threat. Both the inland flooding and tornado threats will continue as the storm continues to slowly move inland.


Hazard data illustrated in the CAT-i map was taken from i-aXs®, Guy Carpenter’s web-based risk management platform. i-aXs users can view impacted areas on any map as well as see how their portfolios were affected. Please contact your broker or GC Analytics (SM) representative for assistance or go to for further information.

The National Hurricane Center (NHC) predicts that Isaac will move northwest into Louisiana today before making a gradual turn to the north by Friday into the state of Arkansas. Areas affected include the lower Mississippi valley, Alabama, Mississippi, Louisiana, and Arkansas by this very large storm. Aggregate losses could add up signicantly for Isaac. Fitch Ratings reported that catastrophe model vendor AIR has issued an insured loss estimate of USD300 million to USD7.5 billion. However, given the event is still ongoing, loss estimates remain highly uncertain.

Storm Details and Forecast Factors

Hurricane Isaac is still a large storm. As of 15:00 UTC, Isaac still maintains an eye, a rather low pressure of 972 mb, maximum sustained winds of 75 mph, and evidence of deep convection on the northern and eastern sectors of the storm. Hurricane force and tropical storm force winds extend outward up to 45 miles and 175 miles from the center, respectively. The radar signature of the storm is still quite impressive. Steering currents are rather weak, as the storm drifts to the northwest through a weakness in the subtropical ridge. As the western half of the ridge rebuilds, the NHC expects that Isaac will be forced to make a gradual northward turn into Friday, before turning to the east into the weekend. The storm is expected by the NHC to be over Arkansas by Friday. Isaac will slowly weaken now that it has moved inland. The NHC expects that Isaac should be downgraded to a tropical storm before the end of the day, and to a depression sometime Thursday, before the storm eventually loses its tropical characteristics during or after the weekend.

Watches and Warnings

As of 15:00 UTC, (11AM EDT, 10AM CDT)

  • Hurricane Warnings have been posted by the NHC for areas including Morgan City, Louisiana to the Alabama-Mississippi border, including Lake Ponchartrain and Lake Maurepas, and metropolitan New Orleans.
  • Hurricane Watches have been posted by the NHC for Intracoastal City to Morgan City, Louisiana.
  • Tropical Storm Warnings are in effect for the Mississippi-Alabama border to the Alabama-Florida border, and from Morgan City to Sabine Pass, Texas.
  • Tropical Storm Watches have been posted by the NHC for east of High Island, Texas to just west of Sabine Pass.


Wind. Hurricane force winds are an ongoing hazard within hurricane warning areas through this afternoon. High rise structures in New Orleans could experience much higher wind speeds, well in excess of 100 mph (category 2 on the Saffir-Simpson scale), at about the 30th story. Tropical storm force winds are occurring or are possible for all areas under a tropical storm watch or warning, and certainly in hurricane-warned areas. Tropical storm conditions at minimum are ongoing or could occur in the immediate term along the west Florida Panhandle, Alabama, Mississippi, Louisiana, and east Texas.

Flooding. Excessive rainfall amounts are expected with accumulations in excess of 7-14 inches from the extreme west Florida Panhandle to southern Louisiana. Local amounts as high as 20 inches are possible with this slow-moving storm. Rainfall amounts of 3-6 inches are expected in Arkansas on Friday. Significant lowland flooding is expected. Inland flooding will be further compounded by rivers backed up by storm surge. Inland flooding will be an ongoing threat for affected areas well into the weekend as the storm slowly moves inland, affecting Mississippi, Louisiana, Alabama, and Arkansas.

Tornadoes. Inland tornadoes will be an ongoing threat to the northern Gulf States today, and tornado warnings have already been issued. Tornadoes will continue to be a threat as the storm moves inland into Louisiana, posing a threat for Mississippi, Alabama, Louisiana, and Arkansas in the coming days.

Storm Surge. A storm surge of 6-12 feet is ongoing in northern Gulf States, including southeast Louisiana and Mississippi. The storm surge is greater than one would expect for a typical category-1 storm, largely due to Isaac’s large windfield, and further amplified by the dramatic bathymetry of the North-Central Gulf. The Northern Gulf coastline is particularly vulnerable to storm surge. The storm surge will further compound inland flooding due to suppressed drainage in river basins. Surge levels as high as eleven feet were reported for certain marine stations, and a surge of five feet was reported at Lake Pontchartrain. Surge levels in excess of eight feet were recently reported in Waveland, Mississippi and Shell Beach, Louisiana. Surge levels should recede as the storm moves inland, but water levels are expected to remain high through the rest of the day.


Storm impacts have included storm surge as high as 11 feet (3 meters), inland flooding of at least 5 inches due to rainfall (and increasing), reports of inland tornadoes, and both tropical storm and hurricane wind speeds. Offshore interests may have sustained damage from the storm, and inland refineries may also sustain damage, in addition to existing disruption due to evacuation and shutdown. This is a large storm, and minor losses aggregated over a large area can be expected. More severe damage and resultant losses can be expected with decreasing distance from the storm center. Evacuations were ordered for many low-lying areas. Schools, universities and businesses are closed for affected areas. Power outages have been reported to hundreds of thousands of customers. Reports of downed trees and powerlines are numerous.


The NHC reported surge levels as high as 11 feet (three meters). Downed trees and power lines were reported, leaving some 390,000 people without power (Entergy Louisiana). More than 4,000 members of the Louisiana National Guard have been mobilized, with 48 boat teams deployed around New Orleans. An estimated 3,000 people were in shelters across Louisiana. Local authorities report storm surge has overtopped a levee in a thinly populated part of Plaquemines Parish, south of New Orleans. Evacuation orders have been issued for areas including St. Bernard and Plaquemines parishes. President Obama has declared a state of emergency for Louisiana, enabling federal support to save lives and protect public health and safety, and Governor Jindal has requested federal aid, all well in advance of landfall. The storm surge has affected a coastal area very vulnerable to storm surge. The remaining surge will also prevent watershed drainage, which will further compound inland flooding in the low-lying areas of southeast Louisiana.


Coast Electric Power Association reported about 14,000 customers without power early Wednesday. Singing River Electric Power Association reported about 1,500 customers without power (Pascagoula). Mississippi Power Co. reported about 3,600 customers without power early this morning (Biloxi). System damage still has yet to be assessed. Low-lying areas along the Mississippi Gulf Coast saw water levels several feet above normal, with storm surges as high as 11 feet. Hancock County Emergency Management Director indicated water up to 4 feet deep in many low-lying areas of Hancock County and still rising. American Red Cross indicated that nearly 2,000 people had entered a total of 33 shelters in Mississippi.


Reports of more than five inches of rain on the Alabama coast, with wind gusts exceeding 47 mph (76 km/hr). Power outages were reported to some residents.


Texas opened a shelter for possible Louisiana evacuees. Governor Rick Perry placed state and local emergency management officials on alert, and also activated a disaster district committee to help those who may evacuate from neighboring Louisiana. Federal emergency officials have started staging relief supplies in neighboring Louisiana.


Energy firms await storm passage before restarting offshore production and oil refineries. 30-foot wave action and resulting undercurrents may have caused damage to offshore refineries, and damage assessments will also have to await storm passage. This could impose further disruption to oil refining throughput. The U.S. Department of Energy estimated about 936,000 barrels per day or 12 percent of oil refining capacity had come offline on the Gulf Coast. The U.S. Bureau of Safety and Environmental Enforcement said that about 93 percent of oil and 67 percent of natural gas production was disrupted by Isaac. The Gulf of Mexico accounts for about 23 percent of U.S. oil production and 7 percent of natural gas output, according to the U.S. Energy Information Administration. About 30 percent of U.S. natural gas processing plant capacity and 44 percent of the country’s oil refining capacity also line the Gulf Coast. The storm could cause ongoing impacts to low-lying fuel refineries along the Gulf Coast, accounting for about 40 percent of U.S. refining capacity.

Source: National Hurricane Center (NOAA), Storm Prediction Center (NOAA),Fitch Ratings, National Weather Service (NOAA), Associated Press, Agence France and Reuters.

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Guy Carpenter publishes CAT-i reports for major natural catastrophes worldwide. These reports cover catastrophes including worldwide tropical cyclones, earthquakes, major UK and European floods and any other natural event that is likely to incur a significant loss to the (re)insurance industry. Please email if you wish to be added to the free email distribution list.

Guy Carpenter compiles RISK-i reports for major technological or man-made events worldwide. These reports cover risks to property, transport and life including explosions, fires, crashes, engineering disasters and terrorist attacks that are likely to incur a significant loss to the (re)insurance industry. Please email if you wish to be added to the free email distribution list.

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