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| #213017 (Received by flhurricane at: 10:58 PM 02.Sep.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 25 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 PM EDT TUE SEP 02 2008 THE LAST COUPLE OF FIXES FROM THE RECONNAISSANCE AIRCRAFT INDICATED THAT HANNA WAS MOVING SLOWLY EASTWARD. IT SEEMS THAT HANNA IS MAKING A SMALL COUNTER-CLOCKWISE LOOP BETWEEN HISPANIOLA AND THE SOUTHEASTERN BAHAMAS. I HAVE TO GIVE SOME CREDIT TO THE GFDL AND HWRF MODELS WHICH PREDICTED THIS LOOP A FEW DAYS AGO... HOWEVER THEY INDICATED THAT HANNA WOULD BE A LITTLE FURTHER NORTH WHEN IT OCCURRED. SINCE THE AIRCRAFT DEPARTED HANNA THE CLOUD PATTERN HAS CONTINUED TO DEGRADE...AND IT IS POSSIBLE THAT HANNA HAS WEAKENED EVEN MORE. HOWEVER...WE WILL KEEP THE INITIAL INTENSITY AT 55 KT SINCE ANOTHER AIRCRAFT IS SCHEDULED TO INVESTIGATE THE STORM AROUND 0600 UTC. STRONG NORTHWESTERLY UPPER-LEVEL WINDS CONTINUE TO SHEAR HANNA. BUT...THE GLOBAL MODELS FORECAST AN UPPER-LEVEL LOW TO CUT-OFF TO THE NORTHWEST OF HANNA VERY SOON...AND THERE IS SOME EVIDENCE IN WATER VAPOR IMAGERY THAT THIS IS BEGINNING TO OCCUR. AS THE UPPER-LOW CUTS-OFF IT IS FORECAST TO DROP SOUTHWARD WHICH SHOULD TURN THE UPPER-FLOW OVER THE STORM FROM THE SOUTH AND SOUTHEAST... WHICH WOULD BE MORE FAVORABLE FOR STRENGTHENING DURING THE NEXT COUPLE OF DAYS. THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND IS CLOSE TO THE CONSENSUS OF THE GUIDANCE. AT 96 HOURS...HANNA WAS MAINTAINED AS A TROPICAL STORM...BECAUSE IT IS PREDICTED TO BE FAIRLY CLOSE TO THE COAST OF THE NORTHEAST UNITED STATES AND THERE COULD STILL BE TROPICAL STORM FORCE WINDS OVER WATER AT THAT TIME. THE TRACK MODELS SUGGEST THAT HANNA WILL BEGIN MOVING NORTHWESTWARD VERY SOON AS THE LARGE UPPER-LEVEL TROUGH OFF THE NORTHEAST UNITED STATES COAST LIFTS NORTHWARD...ALLOWING THE SUBTROPICAL RIDGE OVER THE ATLANTIC TO BUILD WESTWARD. THIS PATTERN IS FORECAST TO STEER HANNA ON A GENERAL NORTHWESTWARD MOTION WITH SOME INCREASE IN FORWARD SPEED OVER THE NEXT COUPLE OF DAYS. SOME OF THE TRACK MODELS HAVE SHIFTED A LITTLE EASTWARD...BUT NOT ENOUGH TO WARRANT A CHANGE TO THE OFFICIAL FORECAST. THE NEW TRACK HAS BEEN ADJUSTED EASTWARD DURING THE FIRST 24-36 HOURS DUE TO THE MORE EASTWARD INITIAL LOCATION...BUT THEREAFTER IT REMAINS VERY CLOSE TO THE PREVIOUS ADVISORY. AS A REMINDER...ONE SHOULD NOT FOCUS ON THE EXACT TRACK AS SMALL DEVIATIONS LEFT OR RIGHT WOULD HAVE LARGE IMPLICATIONS ON BOTH THE TIME AND LOCATION OF LANDFALL. A G-IV MISSION WAS FLOWN THIS EVENING AND THE DATA GATHERED BY THIS AIRCRAFT SHOULD GET ASSIMILATED INTO THE 0000 UTC MODEL GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 03/0300Z 20.5N 72.4W 55 KT 12HR VT 03/1200Z 21.3N 72.3W 55 KT 24HR VT 04/0000Z 22.8N 73.6W 60 KT 36HR VT 04/1200Z 24.4N 75.5W 65 KT 48HR VT 05/0000Z 26.4N 77.4W 70 KT 72HR VT 06/0000Z 32.5N 80.5W 75 KT...INLAND 96HR VT 07/0000Z 41.0N 75.5W 35 KT...INLAND 120HR VT 08/0000Z 50.0N 60.0W 35 KT...EXTRATROPICAL $$ FORECASTER BROWN/AVILA |
