Tropical Storm GAMMA

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TROPICAL STORM GAMMA DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
10 PM EST SAT NOV 19 2005
 
INTERMITTENT AND SMALL BURSTS OF DEEP CONVECTION HAVE BEEN OCCURRING
MAINLY TO THE NORTH OF THE LOW LEVEL CENTER DURING THE PAST FEW
HOURS.  FAIRLY STRONG WIND SHEAR CONTINUES TO DISPLACE THE
CONVECTION AWAY FROM THE CENTER AND PROHIBIT IT FROM PERSISTING.
THE LOW-LEVEL CENTER HAS BECOME MOSTLY OBSCURED IN INFRARED
IMAGERY... BUT ITS ESTIMATED LOCATION RELATIVE TO THE DOWNSHEAR
CONVECTION IS CONSISTENT WITH AN EXTRAPOLATED POSITION BASED ON THE
EARLIER AIRCRAFT POSITIONS.  THE MOTION DURING THE PAST FEW
HOURS HAS BEEN NORTHEASTWARD OR ABOUT 050/5... BUT THIS MOTION MIGHT
NOT YET BE DEFINITIVE.  A GENERAL NORTH-NORTHEASTWARD MOTION IS
FORECAST DURING THE NEXT 24 HOURS OR SO WHILE GAMMA IS WEST OF A
WEAK MID-LEVEL RIDGE AND WHILE THE LOW-LEVEL CENTER IS DRAGGED
ALONG BY THE CONVECTION SHEARED FROM THE SOUTH-SOUTHWEST.
 
THE UPPER-LEVEL TROUGH CURRENTLY OVER THE CENTRAL UNITED STATES IS
FORECAST BY ALL OF THE DYNAMICAL MODELS TO DEEPEN AND MOVE TO THE
SOUTHEAST DURING THE NEXT COUPLE OF DAYS.  THE MODELS ALSO CONTINUE
TO FORECAST THE ASSOCIATED DEVELOPMENT OF AN EXTRATROPICAL LOW
PRESSURE SYSTEM OVER THE EXTREME SOUTHEASTERN U.S. OR NORTHEASTERN
GULF OF MEXICO WITHIN THE NEXT 36 HOURS OR SO.  AS THIS SYSTEM THEN
MOVES UP THE EAST COAST OF THE U.S... A COLD FRONT SHOULD MOVE INTO
THE CARIBBEAN SEA IN 2-3 DAYS... WITH GAMMA ADVANCING AHEAD OF THAT
FRONT.  SEVERAL OF THE MODELS... INCLUDING THE GFS... GFDL... AND
NOGAPS... FORECAST GAMMA TO MEANDER NORTHWESTWARD UNTIL THE FRONT
ARRIVES IN THE CARIBBEAN... AND THEN CALL FOR A MUCH WEAKER OR
POSSIBLY DISSIPATING GAMMA TO MOVE EASTWARD TO THE SOUTH OF CUBA. 
ONE PROBLEM WITH THESE MODELS IS THAT THEY DO NOT INITIALIZE THE
POSITION OR NORTHEASTWARD MOTION OF GAMMA VERY WELL... SO THEIR
EVENTUAL THEIR TRACKS TO THE EAST COULD BE TOO SLOW.  THE OFFICIAL
TRACK FORECAST IS EAST OF MOST OF THE MODELS DURING THE FIRST 36
HOURS... BUT THEREAFTER IT GENERALLY FOLLOWS THE MODEL TRENDS IN
ANTICIPATING A WEAKENING GAMMA TO MOVE EASTWARD ACROSS SOUTHERN
CUBA AHEAD OF THE FRONT THAT PROBABLY WILL EVENTUALLY ABSORB IT.
 
NO FURTHER STRENGTHENING OF GAMMA IS FORECAST... SINCE THE WIND
SHEAR IS ONLY EXPECTED TO INCREASE OVER THE WESTERN CARIBBEAN AS
THE MID-LATITUDE TROUGH PROCEEDS TOWARD THE EASTERN U.S. AND THE
GULF OF MEXICO DURING THE NEXT COUPLE OF DAYS.  THE SHIPS GUIDANCE
FORECASTS STEADY WEAKENING... ONLY HOLDING ON TO TROPICAL STORM
STRENGTH FOR ABOUT 24 MORE HOURS.  THE GFDL FORECAST OF
INTENSIFICATION TO ABOUT 60 KT WITHIN THE NEXT TWO DAYS IS
DISCOUNTED DUE TO THE ESTABLISHED TRACK RECORD OF THAT MODEL
OVER-INTENSIFYING SYSTEMS IN A STRONGLY SHEARED ENVIRONMENT.  THE
NEW OFFICIAL FORECAST DOES NOT QUITE SHOW THE RATE OF WEAKENING
THAT THE SHIPS GUIDANCE DOES... BUT IT IS A DOWNWARD ADJUSTMENT
COMPARED TO THE PREVIOUS ADVISORY.  GAMMA COULD WEAKEN FASTER THAN
FORECAST AND PERHAPS DISSIPATE BEFORE IT EVER BECOMES ENTANGLED
WITH THE COLD FRONT.
 
 
FORECASTER KNABB
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/0300Z 16.6N  84.5W    40 KT
 12HR VT     20/1200Z 17.3N  84.2W    40 KT
 24HR VT     21/0000Z 18.4N  84.1W    35 KT
 36HR VT     21/1200Z 19.5N  83.1W    35 KT
 48HR VT     22/0000Z 20.7N  80.6W    35 KT
 72HR VT     23/0000Z 21.0N  73.0W    30 KT...EXTRATROPICAL
 96HR VT     24/0000Z...ABSORBED BY FRONT
 
 
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