Tropical Storm HANNA

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TROPICAL STORM HANNA DISCUSSION NUMBER  29
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
1100 PM EDT WED SEP 03 2008
 
HANNA HAS BEEN A TENACIOUS TROPICAL CYCLONE. SINCE ITS FORMATION IT
HAS FOUGHT TWO UPPER-LEVEL LOWS...STRONG NORTHERLY SHEAR AND THE
EFFECTS OF LAND. FURTHERMORE...AT TIMES HANNA HAS RESEMBLED A
SUBTROPICAL CYCLONE.  SURFACE AND AIRCRAFT OBSERVATIONS TONIGHT
CONTINUE TO SHOW THAT HANNA HAS A LARGE CIRCULATION AND SATELLITE
IMAGES SUGGEST THAT THE SHEAR IS DECREASING AND HANNA IS DEVELOPING
UPPER-LEVEL OUTFLOW. THESE CHANGES IN THE UPPER FLOW OVER HANNA
HAVE BEEN ACCURATELY FORECAST BY MOST OF THE NUMERICAL WEATHER
PREDICTION MODELS.  THE INITIAL INTENSITY IS 55 KNOTS...AND IS
BASED ON A 68 KT FLIGHT-LEVEL WIND MEASURED AS THE PLANE DEPARTED
THE CYCLONE. WITH THE MORE FAVORABLE UPPER-LEVEL ENVIRONMENT...SOME
INTENSIFICATION IS INDICATED IN THE OFFICIAL FORECAST.  HANNA IS
FORECAST TO REGAIN HURRICANE STATUS IN A DAY OR TWO BUT IT COULD
OCCUR EARLIER. NONE OF THE GUIDANCE INTENSIFIES HANNA BEYOND 70
KNOTS.   

THE CENTER HAS BEEN ROTATING AROUND A LARGE CYCLONIC GYRE AND FIXES
FROM THE RECONNAISSANCE PLANE AND DATA FROM A NOAA BUOY SUGGEST
THAT THE INITIAL MOTION IS 335/11. SOME OF THIS MOTION COULD HAVE
RESULTED FROM REFORMATION OF THE CENTER. SINCE THE SUBTROPICAL RIDGE
IS EXPANDING TO THE NORTHEAST OF HANNA...A NORTHWEST MOTION SHOULD
CONTINUE DURING THE NEXT DAY OR TWO WITH A GRADUAL TURN TO THE
NORTH AROUND THE WESTERN EDGE OF THE HIGH.  THE TRACK
MODELS ARE NOT TIGHTLY CLUSTERED AND THE CONFIDENCE IN THE TRACK
FORECAST IS NOT VERY HIGH. HOWEVER...THE MIDDLE OF THE GUIDANCE
ENVELOPE HAS HANNA MOVING OVER OR VERY CLOSE TO THE COAST OF THE
CAROLINAS.  BECAUSE HANNA IS A LARGE CYCLONE...A HURRICANE WATCH
WILL LIKELY BE REQUIRED FOR A PORTION OF THE SOUTHEASTERN UNITED
STATES COAST EARLY THURSDAY. 

A NOAA JET HAS SAMPLED THE ENVIRONMENT TONIGHT AND THE DATA IS BEING
USED TO INITIALIZE THE 00Z GLOBAL MODEL RUNS. 
 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      04/0300Z 23.2N  72.1W    55 KT
 12HR VT     04/1200Z 24.7N  73.1W    55 KT
 24HR VT     05/0000Z 26.9N  75.0W    60 KT
 36HR VT     05/1200Z 29.3N  77.3W    65 KT
 48HR VT     06/0000Z 32.0N  79.0W    70 KT
 72HR VT     07/0000Z 39.5N  74.0W    50 KT...INLAND
 96HR VT     08/0000Z 46.5N  63.0W    35 KT...EXTRATROPICAL
120HR VT     09/0000Z 49.0N  47.0W    35 KT...EXTRATROPICAL
 
$$
FORECASTER AVILA
 
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