Hurricane Isaac continues to organize as it nears landfall

Isaac gained hurricane status this afternoon after hurricane hunters found winds of 76 mph and a minimum central pressure of 975 mb, and continues to become more organized. In their 5pm EDT update, the National Hurricane Center said Isaac has maximum sustained winds of 80 mph, and is moving northwest at 8 mph--a slow down from yesterday at this time. Satellite loops show that Isaac has gained thunderstorm activity on the southeast side, but is battling dry air to the north. Isaac still appears to be forming an eye wall, though is struggling to do so. Winds have been increasing as Isaac approaches, up to 60 mph has been recorded by buoys close to the shore. Winds off Lake Pontchartrain have varied around 35 mph from the northwest this afternoon. So far New Orleans (KMSY) is seeing wind gusts up to 40 mph, with light rain.


Figure 1. Isaac imagery from the high resolution Terra satellite at 12:30pm EDT, just before becoming a hurricane.

Some rain and thunderstorm activity has reached the northern Gulf Coast this afternoon, with Isaac just over 100 miles southeast of New Orleans. Radar shows thunderstorms from Pensacola to New Orleans. Storm surge has begun to impact the coast, as well, particularly in Mississippi and Louisiana, where reports are that water is "up to cars" in some areas. Many streets are closed in Ocean Springs and Pascagoula, Florida due to surge flooding.

Water levels so far (above mean):

• Shell Beach, LA: 8 feet
• New Canal Station (New Orleans): 2.7 feet
• Bay St. Louis, MS: 5.6 feet
• Pascagoula, MS: 4.4 feet
• Dauphin Island, AL: 3.7 feet

Hurricane Isaac will likely make landfall tonight as a category 1 around midnight CDT, but will still have enough energy and warm water available to maintain hurricane strength for a few hours inland. Isaac will likely continue to strengthen a bit before landfall, but given the large wind field, rapid intensification is unlikely. The storm surge threat could then continue along the Louisiana, Mississippi, Alabama coasts through mid-afternoon on Wednesday, as winds will continue to blow from the east, and then from south, as the storm moves northwest past New Orleans. Should the peak surge coincide with peak tide, the highest storm surge, anywhere from 6 to 12 feet, is expected in Louisiana and Mississippi. Alabama could see a storm surge around 4 to 8 feet.


Figure 2. Rainfall forecast from the HPC through Sunday morning. The lime green bullseye over Gulfport, MS is a value of 15+ inches.

The Hydrometeorological Prediction Center is forecasting around 15 inches of rain to fall around Gulfport, Mississippi, and up to 12 inches of rain to fall near New Orleans, Louisiana by Sunday morning. As Isaac tracks north after landfall, it will bring some much-needed rain to the drought-stricken Mississippi Valley region, particularly west of the Mississippi River. While anywhere from 3-5 inches of rain is expected from Arkansas to Indiana by Sunday, and the Arkansas, Missouri, and Illinois drought will benefit, this is not a drought buster. The driest parts of the country are in the Central Plains states, and this rain will be too little to have a meaningful impact.

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Angela