Hurricane ISAAC

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HURRICANE ISAAC DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092006
1100 PM EDT SUN OCT 01 2006
 
CONVENTIONAL SATELLITE IMAGERY INDICATES THAT ISAAC IS GRADUALLY
WEAKENING. THE EYE FEATURE IS NO LONGER EVIDENT AND THE DEEP
CONVECTION IS BECOMING LESS SYMMETRIC ABOUT THE CIRCULATION CENTER.
THE INITIAL INTENSITY IS LOWERED TO 65 KT BASED ON A BLEND OF THE
LATEST DVORAK DATA T AND CI NUMBERS. THE OVERALL INTENSITY FORECAST
REASONING REMAINS ESSENTIALLY UNCHANGED. ISAAC WILL SOON BE
ENCOUNTERING A SHARP GRADIENT IN SST AS IT CROSSES THE NORTH WALL
OF THE GULF STREAM IN 6-12 HOURS. ADDITIONALLY...THE CYCLONE WILL
BE ENCOUNTERING INCREASING SOUTHWESTERLY SHEAR. THESE ENVIRONMENTAL
FACTORS SHOULD RESULT IN WEAKENING AND A LOSS OF TROPICAL
CHARACTERISTICS DURING THE NEXT 24 HOURS. RESTRENGTHENING OF ISAAC
AS AN EXTRATROPICAL CYCLONE APPEARS UNLIKELY...SINCE MUCH OF THE
AVAILABLE BAROCLINIC ENERGY WILL BE UTILIZED BY ANOTHER LOW
PRESSURE SYSTEM CURRENTLY FORMING OFF THE NEW ENGLAND COAST. GIVEN
ISAAC'S RELATIVELY SMALL SIZE...THE OFFICIAL FORECAST ASSUMES ISAAC
WILL BE ABSORBED BY THE LARGER BAROCLINIC LOW WITHIN 2-3 DAYS.
REGARDLESS OF THE EXACT EVOLUTION OF ISAAC...IT IS EXPECTED TO
AFFECT NEWFOUNDLAND TOMORROW WITH THE POTENTIAL FOR WINDS OF
TROPICAL STORM STRENGTH.
 
ISAAC IS ACCELERATING NORTH-NORTHEASTWARD WITH AN INITIAL MOTION
ESTIMATE OF 020/23 KT.  THE CYCLONE IS EXPECTED TO TURN TOWARD THE
NORTHEAST DURING THE NEXT 24 HOURS...TAKING THE SYSTEM OVER OR VERY
NEAR NEWFOUNDLAND TOMORROW. GUIDANCE IS GENERALLY IN GOOD AGREEMENT
ON THIS SCENARIO...FOLLOWED BY A TURN TOWARD THE EAST-NORTHEAST AS
THE CYCLONE PULLS AWAY FROM NEWFOUNDLAND. THE NEW OFFICIAL FORECAST
IS SHIFTED A LITTLE EAST TOWARD THE MODEL CONSENSUS...AND IS
SLIGHTLY FASTER THAN THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0300Z 38.6N  58.8W    65 KT
 12HR VT     02/1200Z 42.5N  57.2W    60 KT...BECOMING EXTRATROPICAL
 24HR VT     03/0000Z 47.8N  53.5W    50 KT...EXTRATROPICAL
 36HR VT     03/1200Z 51.5N  49.3W    45 KT...EXTRATROPICAL
 48HR VT     04/0000Z 53.3N  45.5W    45 KT...EXTRATROPICAL
 72HR VT     05/0000Z...ABSORBED
 
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FORECASTER RHOME/KNABB
 
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