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| #213309 (Received by flhurricane at: 5:03 PM 03.Sep.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 28 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 500 PM EDT WED SEP 03 2008 AN ASCAT PASS FROM 14Z REVEALED THAT THE LOW-LEVEL CIRCULATION OF HANNA WAS BECOMING ELONGATED IN RESPONSE TO THE ASYMMETRIC DISTRIBUTION OF CONVECTION. IN SPITE OF THIS...DATA FROM THE RECONNAISSANCE AIRCRAFT INDICATE THAT HANNA IS BECOMING A LITTLE BETTER ORGANIZED. TROPICAL STORM FORCE WINDS HAVE RETURNED TO THE SOUTHWEST QUADRANT AND THE PRESSURE HAS FALLEN TO 989 MB. THE AIRCRAFT DATA CONTINUE TO SUGGEST THAT THE MAXIMUM WINDS ARE ABOUT 50 KT. A MORE DEFINITIVE NORTHWARD MOTION HAS COMMENCED...WITH THE INITIAL ESTIMATE BEING 360/10. THE UPPER LOW OFF OF NEW ENGLAND IS BEGINNING TO MOVE OUT...AND AS IT DOES SO MID-LEVEL RIDGING WILL BUILD IN BEHIND IT. HANNA SEEMS TO BE FOLLOWING THE CONVECTION FAIRLY WELL...AND I'VE HAD TO SPEED UP MY PREVIOUS FORECAST A LITTLE BIT. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH A BLEND OF THE ECMWF AND THE GFS. THE HWRF AND GFDL CONTINUE TO BE FASTER THAN THE OFFICIAL FORECAST...AND IF HANNA DEVELOPS FASTER THAN SHOWN BELOW ADDITIONAL TIMING ADJUSTMENTS MAY NEED TO BE MADE. IT'S WORTH NOTING THAT CONNECTING THE 48 AND 72 HOUR FORECAST POINTS WITH A STRAIGHT LINE GIVES A MISLEADING UNDERESTIMATE OF THE THREAT TO THE GEORGIA AND SOUTH CAROLINA COASTS. ONLY A GRADUAL RIGHT TURN IS EXPECTED AFTER 48 HOURS. AS THE UPPER LOW IN THE BAHAMAS AND HANNA SEPARATE...THE SOUTHERLY SHEAR OVER THE CYCLONE WILL TURN SOUTHEASTERLY AND LESSEN. THIS IS EXPECTED TO PROVIDE A MORE FAVORABLE ENVIRONMENT FOR STRENGTHENING...ALTHOUGH NONE OF THE OBJECTIVE AIDS SHOWS VERY MUCH. THE SHIPS AND LGEM BRING THE SYSTEM ONLY TO 60 KT...AND THE HWRF NOT QUITE THAT HIGH. THE OFFICIAL FORECAST IS IN GOOD AGREEMENT WITH THE GFDL WHICH BRINGS HANNA TO 70 KT PRIOR TO LANDFALL. FORECAST POSITIONS AND MAX WINDS INITIAL 03/2100Z 21.9N 71.9W 50 KT 12HR VT 04/0600Z 23.2N 72.7W 55 KT 24HR VT 04/1800Z 25.2N 74.5W 60 KT 36HR VT 05/0600Z 27.4N 76.6W 65 KT 48HR VT 05/1800Z 30.0N 78.5W 70 KT 72HR VT 06/1800Z 36.8N 76.9W 50 KT...INLAND 96HR VT 07/1800Z 44.5N 67.0W 35 KT...EXTRATROPICAL 120HR VT 08/1800Z 48.0N 55.0W 35 KT...EXTRATROPICAL $$ FORECASTER FRANKLIN |
