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#212610 (Received by flhurricane at: 11:01 PM 01.Sep.2008) TCDAT3 HURRICANE HANNA DISCUSSION NUMBER 21 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 PM EDT MON SEP 01 2008 WHILE THE AREAL COVERAGE OF DEEP CONVECTION HAS DECREASED OVER THE PAST COUPLE OF HOURS...WHAT'S LEFT SHOWS GOOD BANDING IN AGREEMENT WITH RECENT MICROWAVE IMAGERY. THE PINE CAY SURFACE STATION IN THE CAICOS ISLAND SUGGESTS THAT THE PRESSURE HAS FALLEN TO ABOUT 978 MB. THE NORTHERLY FLOW ALOFT...ASSOCIATED WITH THE OUTFLOW FROM GUSTAV...IS CLEARLY NOT MAKING IT INTO THE CENTER OF THE TROPICAL CYCLONE. EVEN SO...ONLY MODEST CHANGES IN INTENSITY ARE ANTICIPATED OVER THE NEXT 24-36 HOURS UNTIL THE UPPER FLOW BEGINS TO REVERSE WHEN MID- TO UPPER-LEVEL RIDGING BUILDS IN OVER THE WESTERN ATLANTIC. THERE IS GOOD AGREEMENT AMONG THE GLOBAL MODELS ON THIS EVOLUTION...WHICH SHOULD CREATE A MORE FAVORABLE PATTERN FOR INTENSIFICATION. THE OFFICIAL INTENSITY FORECAST LIES A LITTLE ABOVE THE PREVIOUS ONE...AND IS CLOSE TO A BLEND OF THE GFDL/HWRF/SHIPS/LGEM GUIDANCE...WITH THE DYNAMICAL MODELS A LITTLE HIGHER AND THE STATISTICAL MODELS A LITTLE LOWER. ONE SHOULD NOT INTERPOLATE A PRESUMED LANDFALL INTENSITY FROM THE 72 AND 96 HOUR FORECAST POINTS...AS SOME ADDITIONAL STRENGTHENING COULD OCCUR BETWEEN 72 HOURS AND LANDFALL. THERE HAS BEEN NO AIRCRAFT RECONNAISSANCE THIS EVENING AND PRECISE LOCATION OF THE CENTER IS DIFFICULT. IT APPEARS THAT THE CENTER HAS BEEN MEANDERING...FIRST APPROACHING THE STATION AT PINE CAY BUT IN RECENT HOURS MOVING AWAY AS THE WINDS AT THAT STATION HAVE INCREASED TO 58 MPH IN THE LAST HOUR. WITH NO DEFINITIVE TREND YET ESTABLISHED...THE INITIAL MOTION IS ESTIMATED TO BE STATIONARY. HANNA IS CURRENTLY BLOCKED BY HIGH PRESSURE EXTENDING SOUTHWARD FROM THE GREAT LAKES...BUT THIS FEATURE IS FORECAST BY THE GLOBAL MODELS TO WEAKEN AND SHIFT EASTWARD. AS HIGH PRESSURE DEVELOPS OVER THE WESTERN ATLANTIC OVER THE NEXT 2 TO 3 DAYS...A NORTHWESTWARD TRACK FOR HANNA IS EXPECTED TO DEVELOP. WITH THE EXCEPTION OF THE UKMET...THE MODEL GUIDANCE IS REMARKABLY WELL CLUSTERED. THE OFFICIAL FORECAST IS ADJUSTED SLIGHTLY TO THE EAST OF THE PREVIOUS ADVISORY AND IS ONLY SLIGHTLY TO THE LEFT OF THE GFS...GFDL...AND HWRF. THE UKMET STILL IS THE LEFT-MOST OUTLIER...SHOWING MORE OF A SOUTHWESTWARD MOTION INITIALLY AND A TRACK CLOSER TO THE FLORIDA PENINSULA...ALTHOUGH IT IS WORTH NOTING THAT THE 18Z UKMET SHOWS LESS OF THIS INITIAL SOUTHWESTWARD JUMP THAN THE FULL RUN FROM 12Z. FORECAST POSITIONS AND MAX WINDS INITIAL 02/0300Z 21.8N 72.5W 70 KT 12HR VT 02/1200Z 21.8N 72.8W 75 KT 24HR VT 03/0000Z 22.0N 73.3W 75 KT 36HR VT 03/1200Z 22.8N 74.0W 80 KT 48HR VT 04/0000Z 24.0N 75.0W 85 KT 72HR VT 05/0000Z 28.0N 78.0W 90 KT 96HR VT 06/0000Z 34.0N 80.5W 65 KT...INLAND 120HR VT 07/0000Z 41.5N 77.0W 30 KT...REMNANT LOW $$ FORECASTER FRANKLIN |