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SUBTROPICAL STORM GUSTAV DISCUSSION NUMBER   5
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT MON SEP 09 2002

VISIBLE IMAGERY THIS MORNING SHOWS THAT THE LOW-LEVEL CENTER
OF GUSTAV IS PARTLY EXPOSED ON THE EASTERN EDGE OF THE DEEP
CONVECTION.  REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT INDICATE THAT THERE IS AT BEST ONLY A WEAK WARM CORE WITH
THE SYSTEM AT 850 MB AND THAT THE RADIUS OF MAXIMUM WINDS IS ON THE
ORDER OF 75-100 N MI.  THUS...GUSTAV REMAINS A 40 KT SUBTROPICAL
STORM WITH A CENTRAL PRESSURE OF 1002 MB.
 
THE INITIAL MOTION IS 300/9.  GUSTAV IS CURRENTLY ON THE SOUTH
SIDE OF A LARGE DEEP-LAYER RIDGE OVER THE EASTERN UNITED STATES.
LARGE-SCALE GUIDANCE AGREES THAT THE RIDGE WILL COLLAPSE OVER
THE NEXT 36-48 HR AS TROUGH AMPLIFICATION AND ASSOCIATED SURFACE
CYCLOGENESIS BEGINS OVER THE NEW ENGLAND STATES AND THE CANADIAN
MARITIMES.  TRACK FORECAST GUIDANCE RESPONDS TO THESE FORECASTS
BY CALLING FOR GUSTAVE TO MAKE A RIGHT TURN AS IT NEARS THE
NORTH CAROLINA COAST.  THE BIGGEST QUESTION...AS USUAL...IS THE
TIMING OF THE TURN.  THE FORECAST TRACK IS AN UPDATE OF THE PREVIOUS
PACKAGE...CALLING FOR GUSTAVE TO RECURVE OFFSHORE IN AGREEMENT WITH
MOST GUIDANCE.  HOWEVER...ANY DEVIATION TO THE LEFT OF THE FORECAST
TRACK COULD ALLOW THE CENTER TO REACH THE NORTH CAROLINA COAST
BEFORE THE TURN...OR POSSIBLY EVEN THE SOUTH CAROLINA COAST AS
FORECAST BY THE EXTREME LEFT OUTLIER ETA MODEL.

WHILE THERE IS GOOD TO EXCELLENT OUTFLOW OVER THE WESTERN
SEMICIRCLE...GUSTAVE APPEARS TO BE SUFFERING SOME EASTERLY SHEAR
CAUSED BY THE UPPER-LEVEL LOW TO ITS SOUTH AND SOUTHEAST.  THIS IS
SLOWING THE WRAPPING OF CONVECTION AROUND THE CENTER AND THE
INTENSIFICATION.  LARGE-SCALE MODELS SUGGEST THIS SHEAR SHOULD
GRADUALLY DIMINISH OVER THE NEXT 24 HR...AND THIS SHOULD ALLOW
CONTINUED DEVELOPMENT AND EVENTUAL TRANSITION INTO A TROPICAL
CYCLONE.  AFTER THAT TIME...THE INTENSITY FORECAST BECOMES REALLY
DICEY AS GUSTAV INTERACTS WITH THE DEVELOPING WESTERLIES.  THE
FORECAST WILL CALL FOR THE CYCLONE TO CONTINUE TO INTENSIFY DUE
TO STRONG UPPER-LEVEL DYNAMICS UNTIL IT BECOMES EXTRATROPICAL.
HOWEVER...THERE IS A POSSIBILITY THAT STRONG SHEAR WILL INHIBIT
DEVELOPMENT AFTER 48 HR.

EVEN IF GUSTAV DOES NOT MAKE LANDFALL...IT IS FORECAST TO COME
CLOSE ENOUGH TO THE U. S. COAST TO SPREAD TROPICAL STORM WINDS
AND HEAVY RAINS ONSHORE.

FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     09/1500Z 32.0N  74.0W    40 KTS
12HR VT     10/0000Z 32.8N  75.2W    45 KTS
24HR VT     10/1200Z 34.1N  75.6W    50 KTS
36HR VT     11/0000Z 35.3N  74.7W    55 KTS
48HR VT     11/1200Z 36.6N  72.0W    60 KTS
72HR VT     12/1200Z 41.5N  61.0W    55 KTS...EXTRATROPICAL
 
 
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