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| #213416 (Received by flhurricane at: 11:00 PM 03.Sep.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 29 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 PM EDT WED SEP 03 2008 HANNA HAS BEEN A TENACIOUS TROPICAL CYCLONE. SINCE ITS FORMATION IT HAS FOUGHT TWO UPPER-LEVEL LOWS...STRONG NORTHERLY SHEAR AND THE EFFECTS OF LAND. FURTHERMORE...AT TIMES HANNA HAS RESEMBLED A SUBTROPICAL CYCLONE. SURFACE AND AIRCRAFT OBSERVATIONS TONIGHT CONTINUE TO SHOW THAT HANNA HAS A LARGE CIRCULATION AND SATELLITE IMAGES SUGGEST THAT THE SHEAR IS DECREASING AND HANNA IS DEVELOPING UPPER-LEVEL OUTFLOW. THESE CHANGES IN THE UPPER FLOW OVER HANNA HAVE BEEN ACCURATELY FORECAST BY MOST OF THE NUMERICAL WEATHER PREDICTION MODELS. THE INITIAL INTENSITY IS 55 KNOTS...AND IS BASED ON A 68 KT FLIGHT-LEVEL WIND MEASURED AS THE PLANE DEPARTED THE CYCLONE. WITH THE MORE FAVORABLE UPPER-LEVEL ENVIRONMENT...SOME INTENSIFICATION IS INDICATED IN THE OFFICIAL FORECAST. HANNA IS FORECAST TO REGAIN HURRICANE STATUS IN A DAY OR TWO BUT IT COULD OCCUR EARLIER. NONE OF THE GUIDANCE INTENSIFIES HANNA BEYOND 70 KNOTS. THE CENTER HAS BEEN ROTATING AROUND A LARGE CYCLONIC GYRE AND FIXES FROM THE RECONNAISSANCE PLANE AND DATA FROM A NOAA BUOY SUGGEST THAT THE INITIAL MOTION IS 335/11. SOME OF THIS MOTION COULD HAVE RESULTED FROM REFORMATION OF THE CENTER. SINCE THE SUBTROPICAL RIDGE IS EXPANDING TO THE NORTHEAST OF HANNA...A NORTHWEST MOTION SHOULD CONTINUE DURING THE NEXT DAY OR TWO WITH A GRADUAL TURN TO THE NORTH AROUND THE WESTERN EDGE OF THE HIGH. THE TRACK MODELS ARE NOT TIGHTLY CLUSTERED AND THE CONFIDENCE IN THE TRACK FORECAST IS NOT VERY HIGH. HOWEVER...THE MIDDLE OF THE GUIDANCE ENVELOPE HAS HANNA MOVING OVER OR VERY CLOSE TO THE COAST OF THE CAROLINAS. BECAUSE HANNA IS A LARGE CYCLONE...A HURRICANE WATCH WILL LIKELY BE REQUIRED FOR A PORTION OF THE SOUTHEASTERN UNITED STATES COAST EARLY THURSDAY. A NOAA JET HAS SAMPLED THE ENVIRONMENT TONIGHT AND THE DATA IS BEING USED TO INITIALIZE THE 00Z GLOBAL MODEL RUNS. FORECAST POSITIONS AND MAX WINDS INITIAL 04/0300Z 23.2N 72.1W 55 KT 12HR VT 04/1200Z 24.7N 73.1W 55 KT 24HR VT 05/0000Z 26.9N 75.0W 60 KT 36HR VT 05/1200Z 29.3N 77.3W 65 KT 48HR VT 06/0000Z 32.0N 79.0W 70 KT 72HR VT 07/0000Z 39.5N 74.0W 50 KT...INLAND 96HR VT 08/0000Z 46.5N 63.0W 35 KT...EXTRATROPICAL 120HR VT 09/0000Z 49.0N 47.0W 35 KT...EXTRATROPICAL $$ FORECASTER AVILA |
