Tropical Storm HANNA

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TROPICAL STORM HANNA DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
1100 AM EDT MON SEP 01 2008
 
HANNA'S OVERALL SATELLITE PRESENTATION HAS BEEN IMPROVING THIS
MORNING WITH AN IMPRESSIVE CDO FEATURE NOW COVERING THE LOW-LEVEL
CIRCULATION.  DVORAK SATELLITE INTENSITY ESTIMATES HAVE INCREASED
AND SUGGEST MAX WINDS NEAR 55 KT.  I'M GOING TO CONSERVATIVELY SET
THE INITIAL INTENSITY TO 50 KT SINCE AN AIR FORCE RECONNAISSANCE
AIRCRAFT IS ON ITS WAY.  HAVING SAID THAT...A RECENT QUIKSCAT PASS
SUGGEST THAT THE LOW-LEVEL CIRCULATION COULD BE LOCATED A LITTLE
FARTHER INTO THE DEEP CONVECTION.  THIS SUGGEST THAT HANNA COULD BE
STRONGER THAN ESTIMATED.   THE INTENSITY FORECAST REMAINS TRICKY. 
WATER VAPOR IMAGERY SUGGESTS THAT THE UPPER-LEVEL LOW WHICH HAD
PREVIOUSLY INHIBITED DEVELOPMENT HAS DISSIPATED...AND HANNA NOW
FINDS ITSELF IN A VERY SMALL AREA OF LOW SHEAR.  HOWEVER...WATER
VAPOR IMAGERY ALSO SHOWS STRONG NORTHERLY FLOW ASSOCIATED WITH
GUSTAV'S UPPER-LEVEL OUTFLOW JUST NORTH OF HANNA...AND GLOBAL MODELS
FORECAST MODERATE TO STRONG NORTHERLY SHEAR PERSISTING DURING THE
NEXT DAY OR SO.  GIVEN THE UNCERTAINTY...THE OFFICIAL INTENSITY
FORECAST IS CLOSE TO THE MODEL CONSENSUS AND SHOWS HANNA BECOMING A
HURRICANE A LITTLE SOONER THAN THE PREVIOUS ADVISORY.  BY 72
HOURS...GLOBAL MODELS SUGGEST THE SHEAR COULD WEAKEN...AND HANNA
COULD FIND ITSELF IN A MORE FAVORABLE ENVIRONMENT FOR
STRENGTHENING.  STILL...PREDICTING THE ATMOSPHERIC ENVIRONMENT...
AND TROPICAL CYCLONE INTENSITY...AT DAYS 3-5 IS VERY DIFFICULT. 

WHILE THE CENTER IS DIFFICULT TO LOCATE...HANNA APPEARS TO BE MOVING
MORE TOWARD THE WEST-SOUTHWEST OR 250/4.  A VERY SLOW WEST-
SOUTHWEST OR SOUTHWEST MOTION IS EXPECTED DURING THE NEXT 36 HOURS.  
IN 2 TO 3 DAYS...THE SUBTROPICAL RIDGE IS EXPECTED TO BUILD
WESTWARD OVER THE CENTRAL ATLANTIC CAUSING HANNA TO MOVE
NORTHWESTWARD WITH AN INCREASE IN FORWARD SPEED. THE NEW OFFICIAL
TRACK FORECAST IS ADJUSTED A LITTLE TO THE SOUTH THROUGH 36 HOURS
BASED ON THE LATEST MOTION. TRACK GUIDANCE HAS NOT CHANGED
SIGNIFICANTLY AT THE EXTENDED RANGES AND NEITHER HAS THE OFFICIAL
FORECAST.   
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/1500Z 23.0N  72.9W    50 KT
 12HR VT     02/0000Z 22.8N  73.3W    55 KT
 24HR VT     02/1200Z 22.7N  73.7W    55 KT
 36HR VT     03/0000Z 22.9N  74.1W    60 KT
 48HR VT     03/1200Z 23.7N  74.9W    65 KT
 72HR VT     04/1200Z 26.5N  77.5W    70 KT
 96HR VT     05/1200Z 30.5N  80.5W    70 KT
120HR VT     06/1200Z 36.5N  82.0W    35 KT...INLAND
 
$$
FORECASTER RHOME/AVILA
 
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