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| #211349 (Received by flhurricane at: 11:03 PM 28.Aug.2008) TCDAT2 TROPICAL STORM GUSTAV DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008 1100 PM EDT THU AUG 28 2008 THE CENTER OF GUSTAV HAS BEEN MOVING NEAR OR OVER THE SOUTH COAST OF JAMAICA DURING THE EVENING. SURFACE OBSERVATIONS FROM THE KINGSTON AREA SHOWED WINDS OF TROPICAL STORM FORCE...AND THE LOWEST OBSERVED PRESSURE WAS 990 MB. GUSTAV IS PRODUCING A LARGE AREA OF COLD CONVECTIVE TOPS NEAR AND EAST OF THE CENTER...WITH SATELLITE INTENSITY ESTIMATES OF 65 KT FROM TAFB AND 55 KT FROM SAB. THE INITIAL INTENSITY REMAINS 60 KT. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 270/6...AFTER A SOUTH OF WEST MOTION FOR A FEW HOURS. GUSTAV IS ON THE SOUTH SIDE OF A MID-LEVEL RIDGE OVER FLORIDA AND THE ADJACENT WESTERN ATLANTIC. THE DYNAMICAL GUIDANCE FORECASTS GUSTAV TO TURN NORTHWESTWARD ON THE SOUTHWEST SIDE OF THE RIDGE DURING THE NEXT 48 HR...THEN CONTINUE IN A GENERAL NORTHWESTWARD DIRECTION THROUGH 96 HR. THE GUIDANCE IS RATHER TIGHTLY CLUSTERED DURING THIS TIME PERIOD. AFTER 96 HR...THERE IS SOME SPREAD...AS THE DYNAMICAL MODELS DO NOT AGREE ON WHETHER A RIDGE WILL BUILD TO THE NORTH AND WEST OF GUSTAV. THE GFDL MOVES THE STORM QUICKLY INLAND...WHILE THE LATEST GFS RUN SHOWS IT SLOWING DOWN OVER SOUTHERN LOUISIANA. THE NOGAPS CALLS FOR A LEFT TURN AFTER 96 HR TOWARD THE TEXAS COAST. THE NEW FORECAST TRACK IS AN UPDATE OF THE PREVIOUS PACKAGE THAT IS DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE. THE TRACK IS SHIFTED ONLY SLIGHTLY TO THE LEFT AFTER 72 HR....WITH RELIABLE MODEL FORECASTS REMAINING ON EITHER SIDE OF THE TRACK. SINCE TRACK FORECASTS ARE ALWAYS SUBJECT TO LARGE ERRORS AT 3-5 DAYS...IT IS SIMPLY IMPOSSIBLE AT THIS TIME TO DETERMINE EXACTLY WHERE AND WHEN GUSTAV WILL MAKE FINAL LANDFALL. THE INTENSITY FORECAST IS PROBLEMATIC. GUSTAV IS SHOWING GOOD OUTFLOW IN ALL DIRECTIONS AT THIS TIME...BUT THERE IS EVIDENCE OF NORTHERLY VERTICAL SHEAR UNDERCUTTING THE OUTFLOW. THE LARGE-SCALE MODELS SUGGEST THIS SHOULD SUBSIDE IN ABOUT 24 HOURS...WHICH WOULD ALLOW SIGNIFICANT AND POSSIBLY RAPID INTENSIFICATION OVER THE WARM WATERS OF THE NORTHWESTERN CARIBBEAN. A COMPLICATING FACTOR IS THE UPPER-LEVEL TROUGH CURRENTLY SEEN IN WATER VAPOR IMAGERY OVER THE GULF OF MEXICO. THE LARGE-SCALE MODELS FORECAST THIS FEATURE TO RETREAT WESTWARD AS GUSTAV APPROACHES...WITH HIGH PRESSURE BUILDING OVER THE SOUTHEASTERN GULF. HOWEVER...THE MODELS DO NOT AGREE ON HOW MUCH THE TROUGH WILL MOVE...WITH THE UKMET IN PARTICULAR SHOWING THE POSSIBILITY OF SHEAR AS GUSTAV APPROACHES THE NORTHERN GULF COAST. THE SHIPS MODEL CALLS FOR A PEAK INTENSITY OF 99 KT...THE LGEM MODEL 94 KT...THE GFDL 111 KT...AND THE HWRF 137 KT. THE LATTER IS DEFINITELY NOT OUT OF THE QUESTION. THE INTENSITY FORECAST IS INCREASED OVER THE PREVIOUS FORECAST IN BEST AGREEMENT WITH THE GFDL. HOWEVER...IT WOULD BE NO SURPRISE IF RAPID INTENSIFICATION OCCURRED AND GUSTAV BECAME A CATEGORY 4 OR 5 HURRICANE BY 72 HR. FORECAST POSITIONS AND MAX WINDS INITIAL 29/0300Z 17.8N 77.3W 60 KT 12HR VT 29/1200Z 18.3N 78.6W 60 KT 24HR VT 30/0000Z 19.1N 80.4W 75 KT 36HR VT 30/1200Z 20.4N 82.3W 90 KT 48HR VT 31/0000Z 21.9N 84.2W 100 KT...NEAR COAST OF CUBA 72HR VT 01/0000Z 25.5N 87.5W 110 KT 96HR VT 02/0000Z 28.5N 90.5W 100 KT 120HR VT 03/0000Z 30.0N 92.5W 90 KT...INLAND $$ FORECASTER BEVEN |
