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HURRICANE GERT DISCUSSION NUMBER  32
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SUN SEP 19 1999
 
GERT REMAINS A HEALTHY HURRICANE WITH A 25 NM DIAMETER EYE
SURROUNDED BY VERY COLD CLOUD TOPS. WHILE THE CONVECTION HAS ERODED
A LITTLE IN THE NORTH QUADRANT OVER THE PAST FEW HOURS....DVORAK
INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN AT 127 KT AND 115 KT
RESPECTIVELY.  OBJECTIVE-BASED ESTIMATES ARE RUNNING IN THE SAME
RANGE.  THE INITIAL INTENSITY IS INCREASED TO 115 KT FOR THIS
ADVISORY...AND SOME FLUCTUATIONS IN INTENSITY ARE LIKELY DURING THE
NEXT 24 HRS. SOME GRADUAL WEAKENING OF GERT IS FORECAST LATER IN THE
PERIOD DUE TO INCREASING SHEAR AND SLIGHTLY COOLER WATER. HOWEVER...
THERE IS A POSSIBILITY THAT A JET STREAM APPROACHING FROM THE
NORTHWEST MAY ACT AS AN OUTFLOW MECHANISM RATHER THAN A SHEARING
MECHANISM. IF THAT OCCURS...GERT MAY NOT WEAKEN AT ALL AND MIGHT
STRENGTHEN.
 
THE 12 HOUR MOTION IS 330/8...WHILE A SHORTER TERM MOTION IS CLOSER
TO 315/6. A COMPROMISE INITIAL MOTION OF 325/7 IS USED FOR THIS
PACKAGE. AN UPPER LEVEL LOW LOCATED SEEN IN WATER VAPOR IMAGERY NEAR
21N66W SHOULD HELP KEEP GERT ON A NORTHWEST TRACK FOR THE FIRST PART
OF THE FORECAST PERIOD...FOLLOWED BY A GRADUAL RECURVATURE IN FRONT
OF THE DEVELOPING EASTERN U.S. DEEP LAYER TROUGH. SOME DISAGREEMENTS
HAVE CREPT INTO THE TRACK FORECAST GUIDANCE...WITH THE NOGAPS...
GFDL...AND UKMET MODELS MOVING THE STORM MUCH FASTER THAN THE AVN
AND THE VARIOUS BAM MODELS. THE OFFICIAL FORECAST FOLLOWS A SPEED
THAT IS A COMPROMISE BETWEEN THE FASTER AND SLOWER MODELS.
 
INTERESTS IN BERMUDA SHOULD CONTINUE TO MONITOR THE PROGRESS OF
GERT.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     19/0900Z 24.3N  58.9W   115 KTS
12HR VT     19/1800Z 25.2N  59.8W   115 KTS
24HR VT     20/0600Z 26.4N  61.0W   115 KTS
36HR VT     20/1800Z 27.9N  62.0W   110 KTS
48HR VT     21/0600Z 29.5N  63.0W   105 KTS
72HR VT     22/0600Z 34.0N  62.5W   100 KTS
 
 
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