Hurricane ISAAC

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HURRICANE ISAAC DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
400 PM CDT TUE AUG 28 2012
 
SINCE THE LAST RECON FLIGHTS INTO ISAAC...WHEN A BIAS-CORRECTED SFMR
WIND OF 64 KT WAS OBSERVED...THE RADAR AND SATELLITE APPEARANCE HAS
CONTINUED TO BECOME BETTER DEFINED. ON THIS BASIS...THE ESTIMATED 
INTENSITY HAS BEEN INCREASED TO 70 KT.

TRENDING THROUGH ALL OF THE WIGGLES AND WOBBLES IN THE AIRCRAFT
FIXES YIELDS A GENERAL NORTHWESTWARD MOTION OF 310/07 KT. ISAAC
REMAINS ON TRACK...AND THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE
EARLY PART OF THE FORECAST. ISSAC IS EXPECTED TO CONTINUE
NORTHWESTWARD TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE THAT IS
ORIENTED EAST-WEST ALONG 30N LATITUDE. BECAUSE OF THIS WEAKNESS...
THE STEERING FLOW IS FORECAST TO DECREASE OVER THE NEXT 36-48
HOURS...WHICH WILL RESULT IN ISAAC SLOWING DOWN SOME MORE.
AFTERWARDS...THE RIDGE IS FORECAST TO BUILD BACK IN BY ALL OF THE
MODELS...ALBEIT TO VARYING DEGREES...WHICH SHOULD CAUSE THE CYCLONE
TO TURN SLIGHTLY TOWARD THE WEST-NORTHWEST BEFORE IT TURNS
NORTHWARD BY DAY 4...AND THEN MOVE NORTHEASTWARD INTO THE LOWER
GREAT LAKES AND OHIO VALLEY REGIONS BY DAY 5. IN THE LATTER PART OF
THE FORECAST PERIOD THE FORECAST HAS BEEN NUDGED A LITTLE TO THE
LEFT OF THE PREVIOUS TRACK...BUT REMAINS TO THE RIGHT OF THE
CONSENSUS MODELS THAT HAVE RECENTLY HAD A LEFTWARD BIAS.
 
ALTHOUGH NOT EXPLICITLY FORECAST DUE TO LAND INTERACTION AT 12
HOURS...FAVORABLE WATER TEMPERATURES ALONG WITH AN IMPRESSIVE
UPPER-LEVEL OUTFLOW REGIME SUGGEST THAT ISAAC COULD STRENGTHEN A
LITTLE MORE BEFORE LANDFALL OCCURS.  HOWEVER...BECAUSE OF THE
UNUSUALLY LARGE WIND FIELD...RAPID INTENSIFICATION IS NOT EXPECTED.
 
ISAAC REMAINS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM
SURGE...HEAVY RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE
CENTER AND ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN
GULF COAST. FOR THIS REASON...IT IS IMPORTANT NOT TO FOCUS ON THE
EXACT CENTER LOCATION. THE THREAT OF HEAVY RAINFALL AND FLOODING IS
ALSO EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY
REGION DURING THE NEXT FEW DAYS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/2100Z 28.7N  89.2W   70 KT  80 MPH
 12H  29/0600Z 29.4N  90.0W   70 KT  80 MPH...INLAND
 24H  29/1800Z 30.3N  91.0W   55 KT  65 MPH...INLAND
 36H  30/0600Z 31.3N  91.9W   35 KT  40 MPH...INLAND
 48H  30/1800Z 33.0N  92.5W   30 KT  35 MPH...INLAND
 72H  31/1800Z 36.0N  92.5W   20 KT  25 MPH...INLAND
 96H  01/1800Z 39.0N  90.5W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  02/1800Z 41.5N  86.5W   15 KT  15 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER STEWART
 
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