Wednesday, August 29, 2012

Hurricane Isaac Surprises With Flooding and Storm Surge

Hurricane Isaac isn't the strongest hurricane to hit the Gulf Coast or near New Orleans, but it's creating havoc because the storm is moving so slowly. The winds aren't the problem with the storm, it's the flooding rains and accompanying storm surge while the storm is progressing at a crawl.

The storm surge is higher than models had predicted yesterday. As Jeff Masters notes:
Isaac is bringing large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. At 10 pm EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

6.2' Waveland, MS
9.9' Shell Beach, LA
3.0' Pensacola, FL
4.4' Pascagoula, MS
3.4' Mobile, AL

The 9.9' storm surge at Shell Beach, which is in Lake Borgne 20 miles southeast of New Orleans, exceeds the 9.5' surge recorded there during Category 2 Hurricane Gustav of 2008. Research scientists running a Doppler on Wheels radar located on top of the 16' levees in Plaquemines Parish near Port Sulphur, LA, reported at 8:30 pm EDT that a storm surge of 14' moved up the Mississippi River, and was just 2' below the levees. Waves on top of the surge were cresting over the west side of the levee. Needless to say, they were very nervous. Over the past hour, the surge has retreated some, and waves were no longer lapping over the top of the levee. This is probably due to the fact that we're headed towards low tide. A storm surge of 9.5' has moved up the Mississippi River to the Carrrollton gauge in New Orleans. This is not a concern for the levees in New Orleans, since the storm surge has now brought the river up to 2.5' above its normal water level, which was 7' low due to the 2012 U.S. drought. The highest rise of the water above ground level will occur Wednesday morning over much of Southeast Louisiana, Mississippi, Alabama, and the western Florida Panhandle, when the tide comes back in. It is clear now that this storm surge event will be as dangerous as that of Category 2 Hurricane Gustav of 2008.

Plaquemines Parish is reporting that levees in the area have been overtopped by the storm surge and caused significant flooding. The levees involved aren't part of the network of levees upgraded or built to protect New Orleans following Hurricane Katrina.
The parish levees on the east bank are about 8.5 feet high, and some estimates have storm surge at 13 feet. At daylight, the National Guard is expected to launch a larger rescue effort, coming into the east bank through St. Bernard. After the wind subsides, other water and air rescue efforts likely will launch.

While federal levees in the area appear to be holding, problems in Plaquemines Parish are occurring in areas not protected by the federal system, which was revamped after Katrina.

Guy Laigast, director of the parish's emergency preparedness, says that an 18-mile stretch of the parish east bank back levees might be overtopped from Braithwaite to White Ditch and that some points might be seeing 110 miles per hour winds. There are many varying reports of wind speeds, generally ranging between 80 and 110 miles per hour.

"The devastation of my house is worse than Katrina and the flooding in Woodlawn is worse than Katrina, so those things tell me that the damage on the east bank is worse than Katrina," Plaquemines Parish President Billy Nungesser said this morning.
So far, the New Orleans flood control systems are doing their job and protecting the city from the Mississippi River, the flooding rains, but this storm is going to take a long time before moving away from the region.

Law enforcement has been working to rescue those caught in the flood waters, but private citizens are also busy helping out their neighbors and others stranded by the flooding. One father-son team has already rescued 23 from the rising waters. Parts of the Gulf Coast could see up to 20 inches of rain with 7 to 14 inches falling over a widespread area.

The storm has left hundreds of thousands without power across the Gulf Coast,

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