Hurricane HANNA

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HURRICANE HANNA DISCUSSION NUMBER  22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
500 AM EDT TUE SEP 02 2008
 
CONVENTIONAL AND PASSIVE MICROWAVE SATELLITE IMAGERY INDICATE HANNA
HAS MOVED SOUTHWARD OVER THE PAST 6 HOURS WHILE MAINTAINING A
PRONOUNCED EYE FEATURE IN A 02/203Z AMSU OVERPASS. SATELLITE
INTENSITY ESTIMATES ARE T4.0/65 KT AND T4.5/77 KT FROM TAFB AND
SAB...RESPECTIVELY. THEREFORE...THE INITIAL INTENSITY REMAINS
UNCHANGED AT 70 KT FOR THIS ADVISORY.
 
THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 270/02 KT. LATEST
SATELLITE POSITION ESTIMATES SUGGEST THAT HANNA COULD STILL BE
MOVING SOUTHWARD. HOWEVER...ALL OF THE GLOBAL MODELS ARE NOW IN
EXCELLENT AGREEMENT THAT AN UPPER-LEVEL LOW WILL PINCH OFF TO THE
SOUTH AND WEST OF HANNA DURING THE NEXT 24-36 HOURS...WHICH  IS
EXPECTED TO INDUCE A SLOW NORTH AND THEN NORTHWESTWARD MOTION
ACROSS THE SOUTHEASTERN BAHAMAS. BY 48-72 HOURS...THE SUBTROPICAL
RIDGE TO THE NORTHEAST OF HANNA IS FORECAST TO GRADUALLY BUILD
WESTWARD THROUGH 96 HOURS...WHICH SHOULD INDUCE A FASTER FORWARD
NORTHWESTWARD MOTION TOWARD THE SOUTHEASTERN UNITED STATES. THE
RIDGE AXIS IS FORECAST BY ALL THE MODELS TO GENERALLY EXTEND
EAST-WEST BETWEEN 32-24N LATITUDE...AND THE EXACT TRACK OF HANNA
WILL DEPEND HEAVILY ON HOW FAR SOUTH AND WEST THE CYCLONE MOVES
DURING THE NEXT 36 HOURS...AND ALSO HOW STRONG THE WESTERN PORTION
OF THE RIDGE WILL BE. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE
PREVIOUS ADVISORY AND IS DOWN THE MIDDLE OF THE TIGHTLY CLUSTERED
NHC MODEL GUIDANCE SUITE. HANNA IS FORECAST TO MOVE NORTHWESTWARD
UNTIL IT REACHES THE COAST OF SOUTH CAROLINA...AFTER WHICH IT IS
EXPECTED TO GRADUALLY RECURVE TO THE NORTHEAST. AN APPROXIMATE
84-HOUR POSITION WOULD BE NEAR 31.3N 80.2W.
 
HANNA HAS MAINTAINED A WELL-DEFINED INNER-CORE STRUCTURE BASED ON
THE 0202Z AMSU OVERPASS...AND ANOTHER CDO FEATURE WITH CLOUD TOPS
AS COLD OF -80C TO -87C HAS REDEVELOPED OVER THE CENTER SIMILAR TO
THE THIS TIME LAST NIGHT. THE CURRENT 30-KT NORTHERLY SHEAR PATTERN
IS FORECAST BY ALL THE MODELS TO BEGIN TO WEAKEN TODAY AND CONTINUE
TO WEAKEN DURING THE NEXT 48 HOURS...AND GRADUALLY SWITCH TO A
SOUTHEASTERLY COMPONENT WITH LESS THAN 15 KT OF SHEAR AT 72-96
HOURS. GIVEN THE DEVELOPMENT OF A FAVORABLE UPPER-LEVEL OUTFLOW
PATTERN AND SSTS OF AT LEAST 28C ALONG THE FORECAST TRACK UNTIL
LANDFALL...STEADY INTENSIFICATION SEEMS QUITE REASONABLE. THE
OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY
...AND IS SIMILAR TO THE SHIPS MODEL. IT IS IMPORTANT TO NOTE THAT
HANNA IS EXPECTED TO CONTINUE TO INTENSIFY...OR AT LEAST REMAIN
STEADY...UNTIL LANDFALL OCCURS BETWEEN 84 AND 96 HOURS...RATHER
THAN APPEAR TO BE WEAKENING LIKE SOME AUTOMATIC INTENSITY PLOTTING
SOFTWARE MAY SHOW. IN FACT...BY 84 HOURS HANNA COULD BE A MAJOR
HURRICANE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0900Z 21.3N  72.7W    70 KT
 12HR VT     02/1800Z 21.4N  73.1W    70 KT
 24HR VT     03/0600Z 22.0N  73.5W    75 KT
 36HR VT     03/1800Z 23.0N  74.3W    80 KT
 48HR VT     04/0600Z 24.4N  75.5W    85 KT
 72HR VT     05/0600Z 28.7N  79.0W    90 KT
 96HR VT     06/0600Z 34.7N  80.7W    55 KT...INLAND
120HR VT     07/0600Z 42.5N  74.0W    35 KT...EXTRATROPICAL INLAND
 
$$
FORECASTER STEWART
 
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