Hurricane HANNA

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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
 
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