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#211692 (Received by flhurricane at: 10:50 AM 30.Aug.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 AM EDT SAT AUG 30 2008 HANNA CONTINUES TO PRODUCE A LARGE AREA OF DEEP CONVECTION WITH CLOUD TOP TEMPERATURES BELOW -80 DEGREES C. HOWEVER...THE CENTER OF THE TROPICAL CYCLONE IS LOCATED NEAR THE SOUTHWESTERN EDGE OF THIS CONVECTION. THE EXACT CENTER HAS BEEN DIFFICULT TO LOCATE AS A COUPLE OF SMALL VORTICES HAVE BEEN SEEN ROTATING AROUND THE LARGER CIRCULATION THIS MORNING. SATELLITE INTENSITY ESTIMATES REMAIN T3.0 OR 45 KT AND AN EARLIER QUIKSCAT PASS SUGGEST MAXIMUM WINDS WERE NEAR THAT VALUE. THERE WERE SOME STRONGER WINDS SEEN IN THE QUIKSCAT DATA...BUT THESE WINDS WERE WELL REMOVED FROM THE CENTER AND APPEAR TO HAVE BEEN RAIN-INFLATED. THE SOMEWHAT UNCERTAIN INITIAL MOTION ESTIMATE IS 275/7. HANNA HAS CONTINUED TO MOVE MORE WESTWARD DURING THE PAST 12-24 HOURS...WHICH HAS REQUIRED A LITTLE SOUTHWARD ADJUSTMENT TO THE TRACK FORECAST IN THE SHORT-TERM. THE TRACK GUIDANCE PREDICTS A GENERAL WEST TO WEST-NORTHWEST MOTION DURING THE NEXT 24-36 HOURS. THEREAFTER... THERE IS A GREAT DEAL OF SPREAD AMONG THE MODELS...AS A STRONG HIGH PRESSURE RIDGE BUILDS OVER THE EASTERN UNITED STATES. THE GFDL AND HWRF RESPOND BY SHOWING A VERY SLOW AND ERRATIC MOTION IN ABOUT 3 DAYS...WHILE THE UKMET TURNS HANNA SOUTHWESTWARD TOWARDS EASTERN CUBA. VERY LATE IN THE PERIOD...THE HIGH OVER THE EASTERN U.S. IS FORECAST TO MOVE OFF THE EAST COAST INTO THE WESTERN ATLANTIC AND SEVERAL OF THE FORECAST MODELS NOW INDICATE A WEST-NORTHWESTWARD AROUND DAY 5. THE NEW FORECAST WHICH IS VERY SIMILAR TO THE PREVIOUS ADVISORY...BUT SMOOTHS THROUGH THESE POSSIBLE UNDULATIONS AND SHOWS A SLOW WESTWARD MOTION BETWEEN 72-120 HOURS. THE NEW TRACK IS GENERALLY ALONG OR JUST SOUTH OF THE MODEL CONSENSUS. THE MUCH DISCUSSED UPPER-LOW JUST WEST OF THE STORM APPEARS TO HAVE WEAKENED A LITTLE THIS MORNING. THE SHIPS GUIDANCE SUGGESTS THE WESTERLY SHEAR MAY RELAX JUST A LITTLE OVER THE NEXT 24 HOURS. GIVEN THE RESILIENCE OF HANNA...THE OFFICIAL FORECAST SHOWS A LITTLE STRENGTHENING DURING THE NEXT DAY OR SO. THEREAFTER...STRONG NORTHWEST TO NORTH UPPER-LEVEL WINDS ARE FORECAST...SO THE OFFICIAL INTENSITY FORECAST NOW KEEPS HANNA JUST BELOW HURRICANE STRENGTH. IT SHOULD BE NOTED ONCE AGAIN...THAT THE NHC INTENSITY FORECAST REMAINS BELOW ALL OF THE RELIABLE GUIDANCE. BASED ON THE NEW FORECAST TRACK...THE GOVERNMENT OF THE BAHAMAS HAS ISSUED A TROPICAL STORM WATCH FOR THE SOUTHEASTERN BAHAMAS AND TURKS AND CAICOS ISLANDS. FORECAST POSITIONS AND MAX WINDS INITIAL 30/1500Z 21.9N 66.4W 45 KT 12HR VT 31/0000Z 22.4N 67.9W 50 KT 24HR VT 31/1200Z 22.9N 69.6W 55 KT 36HR VT 01/0000Z 23.2N 71.0W 60 KT 48HR VT 01/1200Z 23.2N 72.1W 60 KT 72HR VT 02/1200Z 23.0N 73.5W 55 KT 96HR VT 03/1200Z 23.0N 75.0W 55 KT 120HR VT 04/1200Z 23.0N 76.5W 55 KT $$ FORECASTER BROWN |