Hurricane Isaac Crawls ashore in Louisiana

Hurricane Isaac Radar Image as of 12:51CDT August 29th 2012 as seen from New Orleans Long Range Radar. The center of the storm was approaching Baton Rouge at this time. Radar image from Wunderground’s radar pages.

Hurricane Isaac crawled inland over the last 12 hours. It made its first landfall near the mouth of the Mississippi River at 6:45pmCDT last night, and a second landfall near Port Fourchon further to the west around 3am CDT as an 80mph, 969mb category one hurricane.

Winds… Numerous reports of hurricane force wind gusts have come in from Louisiana and even some unofficial reports in Mississippi. These include gusts to 74mph in central Lake Pontchatrain, 79mph in Pilottown, 83mph at New Canal tidal station on Lake Pontchatrain, and some unofficial gusts 90-105mph. These winds have caused around half a million power outages and substantial tree damage. Baton Rouge is about to take the eye wall of Hurricane Isaac and gusts could near hurricane force in that city as it passes.

Tropical Storm conditions will continue in Louisiana, Mississippi and Alabama for another 12-24 hours as Isaac only slowly weakens and slowly moves inland.

Rain… Radar estimates show widespread rainfall totals of 6-8inches in parts of Louisiana, and Isaac has a slug of moisture coming off the Gulf of Mexico ready to come in for at least another 24 hours. This means that widespread rainfall totals of 6-14inches are likely with some isolated areas receiving over 20inches. This is going to cause flash flooding, especially in low lying areas fighting off storm surge.

NOAA’s National Data Bouy Center (NDBC) Tidal gauge at Shell Beach, LA showing a peak storm surge of ~11ft.

Storm Surge…A dangerous storm surge has been observed along the northern Gulf Coast, peak observations were made at Shell Beach, LA where a 11.07ft storm surge was observed. Additionally, an 8ft storm surge was observed in Waveland, MS and a 5.4ft surge on lake Pontchatrain, water levels are still rising at these two locations. A storm surge between 3 and 7 feet has been observed from Grand Isle, LA to Pensacola, FL.

Interestingly, the storm surge is pushing up the Mississippi river and causing it to back up. This combined with heavy flooding rains is stressing flood protection levees along the river, and there have been some reports describing levees being overtopped flooding homes and prompting water rescues. This backing up phenomena is being observed even up river past Baton Rouge – hundreds of miles inland. Fortunately, the midwestern drought and heatwave of 2012 has meant that the background river levels were unusually low so flooding isn’t going to be as bad as it would have been otherwise.

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