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| #211442 (Received by flhurricane at: 11:12 AM 29.Aug.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 AM EDT FRI AUG 29 2008 A 1031 UTC QUIKSCAT OVERPASS WAS VERY HELPFUL IN LOCATING THE CENTER OF HANNA EARLY THIS MORNING. VISIBLE IMAGERY SHOWED THAT THE CENTER BRIEFLY BECAME EXPOSED...HOWEVER...NEW CONVECTION FORMED SINCE THAT TIME AND THE CENTER IS POSITIONED JUST BENEATH THE COLDER CLOUD TOPS. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB CONTINUE TO SUPPORT 45 KT...SO THE INITIAL INTENSITY REMAINS UNCHANGED. IN THE NEAR TERM...THE DYNAMICAL MODELS SUGGEST THAT THE UPPER-LOW TO THE WEST-NORTHWEST OF HANNA WILL MOVE WESTWARD AND WEAKEN...WHICH SHOULD RELAX THE SOUTHWESTERLY SHEAR THAT IS CURRENTLY IMPINGING UPON THE CYCLONE. THE INTENSITY FORECAST FOLLOWS THIS SOLUTION AND CALLS FOR GRADUAL STRENGTHENING DURING THE NEXT 2 DAYS... BRINING HANNA TO HURRICANE STATUS. THEREAFTER THERE IS A LARGE AMOUNT OF UNCERTAINTY IN THE INTENSITY FORECAST. THE GLOBAL MODELS PREDICT STRONG NORTHWEST TO NORTH UPPER-LEVEL WINDS OVER HANNA...WHICH ONE WOULD THINK SHOULD HALT ADDITIONAL STRENGTHENING OR EVEN WEAKEN THE STORM. HOWEVER...NEARLY ALL OF THE INTENSITY GUIDANCE SHOW STRENGTHENING OR LITTLE INTENSITY CHANGE DURING THAT TIME. ASSUMING THAT THE SHEAR WILL PRODUCE A NEGATIVE AFFECT ON HANNA...THE NEW INTENSITY FORECAST FOLLOWS PERSISTENCE OF PREVIOUS ADVISORY AND IS A LITTLE BELOW MOST OF THE GUIDANCE. HANNA MOVED WEST-NORTHWESTWARD DURING THE PAST 12 HOURS AND THE INITIAL MOTION ESTIMATE IS 285/10. THE TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH 48 HOURS ON A WEST-NORTHWEST TO NORTHWEST MOTION. THEREAFTER...THE MODELS GENERALLY SHOW A WEST- SOUTHWESTWARD OR SOUTHWARD TURN..SOUTH OF A BUILDING RIDGE OVER THE EASTERN UNITED STATES. HOWEVER...THE SHARPNESS OF THE TURN AND SPEED OF MOTION VARIES GREATLY. THE NEW NHC TRACK HAS BEEN ADJUSTED SOUTHWARD DURING THE FIRST COUPLE OF DAYS...MAINLY DUE TO THE MORE WESTWARD INITIAL MOTION. THIS IS IN CLOSE AGREEMENT WITH THE MODEL CONSENSUS. AFTER 72 HOURS...THE NEW TRACK IS A LITTLE FASTER THAN THE PREVIOUS ADVISORY...BUT IS NOTICEABLY SLOWER THAN THE UKMET AND GFDL MODELS. THE HWRF...WHICH SHOWS A CYCLONIC LOOP NORTH OF THE BAHAMAS AND A NORTHEASTWARD MOTION AT DAY 5...IS CONSIDER AN OUTLIER AT THIS TIME. INTERESTS IN THE SOUTHWESTERN BAHAMAS AND TURKS AND CAICOS SHOULD MONITOR THE PROGRESS OF HANNA. IMPACTS IN THESE AREAS COULD OCCUR MUCH SOONER THAN INDICATED BY THE EXACT TRACK...ESPECIALLY IF THE MORE NORTHWESTWARD MOTION DOES NOT MATERIALIZED LATER TODAY OR ON SATURDAY. FORECAST POSITIONS AND MAX WINDS INITIAL 29/1500Z 21.3N 62.7W 45 KT 12HR VT 30/0000Z 22.2N 64.5W 50 KT 24HR VT 30/1200Z 23.6N 66.7W 55 KT 36HR VT 31/0000Z 24.6N 68.6W 60 KT 48HR VT 31/1200Z 25.1N 70.1W 70 KT 72HR VT 01/1200Z 24.7N 71.6W 65 KT 96HR VT 02/1200Z 24.0N 72.5W 65 KT 120HR VT 03/1200Z 23.0N 73.5W 60 KT $$ FORECASTER BROWN |
