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Hurricane ISAAC (Text)

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HURRICANE ISAAC DISCUSSION NUMBER  16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092006
1100 AM EDT SUN OCT 01 2006
 
THE EYE FEATURE OF ISAAC HAS BECOME MUCH LESS DEFINED OVER THE PAST
SEVERAL HOURS. IT APPEARS THAT SOUTHWESTERLY SHEAR IS BEGINNING TO
HAVE SOME EFFECT ON THE TROPICAL CYCLONE. DVORAK INTENSITY
ESTIMATES ARE BETWEEN 65 AND 75 KT AND AN EARLIER QUIKSCAT PASS
SUPPORTED MAXIMUM WINDS OF ABOUT 70 KT...WHICH IS THE ESTIMATED
INITIAL INTENSITY. ISAAC IS EXPECTED TO GRADUALLY WEAKEN AS IT
ENCOUNTERS INCREASING SHEAR AND MUCH COOLER SSTS DURING THE NEXT
24-36 HOURS. FSU PHASE SPACE DIAGRAMS BASED ON THE GLOBAL MODELS
SHOW THAT ISAAC WILL TRANISITION INTO A EXTRATROPICAL CYCLONE IN
NOT MORE THAN 24-36 HOURS.
 
THE CURRENT MOTION IS 355/11. IT APPEARS THAT ISAAC IS BEGINNING TO
ACCELERATE AND TURN NORTHWARD AHEAD OF THE LARGE DEEP-LAYER TROUGH
THAT IS APPROACHING THE EAST COAST OF THE UNITED STATES. ALL OF THE
GLOBAL MODELS INDICATE THAT THE CYCLONE WILL MOVE OVER OR VERY NEAR
SOUTHEASTERN NEWFOUNDLAND IN ABOUT 36 HOURS. THE GFS AND UKMET
MODELS REMAIN ON THE WESTERN SIDE OF THE GUIDANCE WHILE THE GFDL IS
TO THE EAST AND KEEPS ISAAC OFFSHORE. THE OFFICIAL FORECAST LEANS
TOWARDS THE GFS/UKMET SOLUTION AND IS A LITTLE WEST OF THE GUNA
MODEL CONSENSUS. AFTER PASSING NEWFOUNDLAND...THE MODELS DIVERGE
SIGNIFICANTLY ON WHICH LOW BECOMES DOMINANT...THE EXTRATROPICAL
REMNANT OF ISAAC OR THE BAROCLINIC LOW MOVING OFF THE NORTHEAST
UNITED STATES COAST. THIS FORECAST ASSUMES THE SMALLER ISAAC WILL
BECOME ABSORBED BY THE LARGE BAROCLINIC LOW AND THE 72 HOUR
FORECAST REFLECTS THIS SCENARIO. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/1500Z 34.4N  60.3W    70 KT
 12HR VT     02/0000Z 37.2N  59.8W    70 KT
 24HR VT     02/1200Z 42.0N  57.2W    65 KT
 36HR VT     03/0000Z 47.0N  53.0W    60 KT...EXTRATROPICAL
 48HR VT     03/1200Z 50.5N  48.7W    55 KT...EXTRATROPICAL
 72HR VT     04/1200Z...ABSORBED
 
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FORECASTER BROWN/FRANKLIN
 
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