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| #57678 (Received by flhurricane at: 10:03 PM 19.Nov.2005) TCDAT2 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 |
