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Dry air originally south of tropical storm Isaac has wrapped around to the north side disrupting eye development and thunderstorm activity on the whole north side. Isaac strengthened to about 5 miles per hour short of hurricane but strengthening now appears to have stopped. Isaac may eventually reach hurricane strength, but is  now very unlikely to become a highly destructive major hurricane. It doesn't have time to organize much better before it comes ashore with such a large amount of dry air on its north side. Coastal residents still need to take Isaac seriously because it is a large storm moving a large mass of water. Buoy wave heights maxxed out at 17 feet at buoy 42003. That's not very impressive compared to a major hurricane which would hit 40 feet or higher. Isaac is capable of bringing flash floods and tornadoes to inland areas as it comes ashore, but it doesn't appear to be a major threat to New Orleans.

Water vapor imagery shows dry air wrapped near the core of Isaac on the north side.

The forecast track will take Isaac over water with relatively low heat content. Although surface temperatures are in the mid 80's the warm water isn't very deep along the forecast track. The cool water below the surface will tend to slow development. Hurricane winds tend to pull up water from below the center. Because the warm water isn't very deep along the forecast track, cool water will well up and reduce the potential energy available to Isaac.
Isaac may still strengthen into a category 1 hurricane as it approaches the Mississippi River delta, but this is good news for people who were fearing worse.

10pm CDT UPDATE

Isaac has remained just under hurricane strength for hours but the NHC is forecasting the storm to strengthen to a hurricane at the high end of category 1 before it comes ashore. The engineered structures around New Orleans should be strong enough to protect the city. Obviously, it will be dangerous near landfall and all evacuation orders should be followed.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0300Z 27.1N  87.0W   60 KT  70 MPH
 12H  28/1200Z 28.0N  88.0W   70 KT  80 MPH
 24H  29/0000Z 29.1N  89.2W   80 KT  90 MPH...ON THE COAST
 36H  29/1200Z 29.9N  90.1W   65 KT  75 MPH...INLAND
 48H  30/0000Z 30.7N  90.7W   50 KT  60 MPH...INLAND
 72H  31/0000Z 33.3N  91.7W   30 KT  35 MPH...INLAND
 96H  01/0000Z 37.5N  91.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  02/0000Z 40.5N  87.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

And NHC says 6 to 12 inches of rain is forecast with as much as 18 inches possible.
RAINFALL...ISAAC IS EXPECTED TO PRODUCE TOTAL RAINFALL AMOUNTS OF 6 TO 12 INCHES...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 18 INCHES...IN  SOUTHEASTERN LOUISIANA...SOUTHERN MISSISSIPPI... SOUTHERN ALABAMA AND THE EXTREME WESTERN FLORIDA PANHANDLE.

TORNADOES...ISOLATED TORNADOES ARE POSSIBLE ACROSS WEST-CENTRAL AND NORTHWESTERN FLORIDA THROUGH TONIGHT...AND ALONG THE NORTHERN GULF COAST LATE TONIGHT AND TUESDAY.

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