HURRICANE ISAAC SUMMARY

Overview

Tropical Depression Nine formed in the Atlantic, east of the Lesser Antilles, on the morning of August 21, 2012, and by the afternoon of the 21st had strengthened into Tropical Storm Isaac. Isaac tracked westward through the eastern Caribbean Sea, into the Florida Straits and then into the southeast Gulf of Mexico through the early hours of August 27th, while maintaining high end tropical storm strength. Tropical Storm Isaac then tracked northwest across the eastern Gulf of Mexico late on the 27th and early on the 28th. On the afternoon of August 28th, Isaac strengthened to a hurricane with winds of 80 mph just off the southeast Louisiana coast, about 75 miles south-southeast of the mouth of the Mississippi River. At 6:45 PM CDT on August 28th, Hurricane Isaac made a brief landfall along the coast of Southeast Louisiana in Plaquemines Parish. Maximum sustained winds were 80mph at this landfall. Isaac did not remain over land for long as the hurricane was back over water again by 9 pm that same evening. Isaac made a second landfall along the coast of Southeast Louisiana, just to the west of Port Fourchon, around 2:15 AM CDT August 29th, again with maximum sustained winds of 80mph.

Track of Hurricane Isaac Aug 21-Aug 30 2012
Hurricane Isaac Path
(Image courtesy of University of Wisconsin – Madison Cooperative Institute for Meteorological Satellite Studies)

As the inner core of Isaac moved very slowly north across central Louisiana over the course of August 29th and 30th, the outer fringes of the hurricane lifted northward across portions of southeast Mississippi, southwest Alabama, and the western Florida panhandle. The slow movement of Isaac resulted in prolonged wind, coastal flooding and flash flooding impacts across the region.

http://vortex.nsstc.uah.edu/uahsevere/img/Isaac_72hr.gif
(3-Day Radar Loop via UAH Severe Weather and Radar Research Group)

Coastal Flooding Impacts

While the hurricane was off the southeast Louisiana coast, a strong onshore wind flow over coastal Alabama and the northwestern Florida panhandle resulted in minor to moderate coastal beach erosion and flooding. Storm tides of 4 to nearly 6 feet were observed across the Mobile Bay region, and up to nearly 4 feet farther to the east over portions of the western Florida panhandle. These storm tides resulted in salt-water inundation levels of 1 to 3 feet over many coastal areas of southwest Alabama and the extreme western Florida panhandle, especially at the times of astronomical high tides on both August 28th and 29th. Numerous coastal roadways were flooded, along with many other waterfront properties.

Alabama Port
Alabama Port
Near downtown Mobile
Near downtown Mobile

Pensacola Beach Pier
Pensacola Beach Pier

Mobile Bay Causeway (viewed from I-10)
Mobile Bay Causeway (viewed from I-10)

Heavy Rainfall Impacts

On August 29th and 30th, Isaac moved slowly northward across Louisiana while weakening to a tropical storm and further to a tropical depression. Although the storm weakened in intensity as it moved inland, the movement of the storm slowed to around 5 mph, which resulted in prolonged excessive rainfall and resultant flooding across parts of extreme southwest Alabama and well as all of interior southeast Mississippi. The heaviest, most persistent rainfall occurred on the evening of August 29th. Radar storm total estimates of 10 to nearly 20 inches of rainfall were indicated over parts of the region, especially over much of interior southeast Mississippi. The highest observed regional rainfall total was in Buckatunna, Mississippi, where 15.39 inches (may be some higher amounts in SE MS) of rain fell. This heavy rainfall resulted in considerable flash flooding over much of the region, especially over southeast Mississippi, with many roadways flooded or washed out, some buildings inundated and even a few water rescues of individuals became necessary.

Hurricane Isaac Total Rainfall - Radar Estimated

Washed out road near Leakesville MS
Washed out road near Leakesville MS

Flooding near Leakesville MS
Flooding near Leakesville MS


Washed out road near Lucedale MS
Washed out road near Lucedale MS

Wind Impacts

Wind impacts were rather minimal across the region, but there were some scattered, brief power outages as well as some trees down. The strongest winds occurred along the immediate coast, where the onshore flow produced the highest wind gusts. The highest wind gust observed during Isaac was 60 mph, which occurred at 910 AM CDT, on the east end of Dauphin Island, Alabama. Elsewhere, along the Alabama and western Florida panhandle coastline, peak wind gusts of 40 to 50 mph were common from the late afternoon of Aug 28th through the afternoon of Aug 29th. Some of the higher wind gusts reported are as follows: 51MPH at Brookley Field near downtown Mobile, 47 MPH at the Mobile Regional Airport and at the Pensacola International Airport, 44 MPH at Milton, Florida and 40 MPH at Destin, Florida.

Tornado Impacts

Three brief, weak EF-0 tornadoes occurred across the region as a result of hurricane Isaac. One each in Monroe and Choctaw counties of Alabama, and one in Greene county Mississippi. None produced any significant damage, with only light debris and a few downed and snapped trees reported.

Summary

Overall the region fared well with regard to impacts from Hurricane Isaac. Heavy flooding rains, especially over southeast Mississippi; and minor to moderate coastal flooding and erosion were the primary problems. No injuries were reported in association with Hurricane Isaac across the area, but one indirect death was reported in Escambia county Florida, when a man apparently drowned in the increasingly rough surf while attempting to ride a JetSki on Aug 27th, as Isaac began moving north across the Gulf.

To see the Post Tropical Cyclone Report for Hurricane Isaac issued by the National Weather Service in Mobile, please go to - http://www.srh.noaa.gov/mob/?n=isaac_psh


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