Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  32
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SAT SEP 13 2003
 
SATELLITE IMAGES SHOW THAT CLOUD TOPS HAVE WARMED OVER THE PAST 6
HOURS AND ISABEL MAY HAVE WEAKENED A LITTLE.  BUT SINCE THE PREVIOUS
ADVISORY VALUE OF 140 KNOTS WAS BASED ON AIRCRAFT RECONNAISSANCE
AND THE NEXT RECONNAISSANCE MISSION IS AT 06Z...THE OFFICIAL WIND
SPEED IS KEPT THE SAME AS THE PREVIOUS ADVISORY VALUE OF 140 KNOTS.
 
THE GLOBAL MODELS GENERALLY SHOW LITTLE CHANGE IN WIND SPEED FOR 5
DAYS BUT THE SHIPS STATISTICAL DYNAMICAL MODEL GRADUALLY WEAKENS
ISABEL TO 70 KNOTS IN 5 DAYS...AS A RESULT OF INCREASING VERTICAL
SHEAR AND CLIMATOLOGY AMONG OTHER FACTORS.  THE OFFICIAL FORECAST IS
FOR WEAKENING TO 100 KNOTS IN 5 DAYS...A COMPROMISE BETWEEN SHIPS
AND THE GLOBAL MODELS.
 
THE INITIAL MOTION IS 290/11 BASED ON THE PAST 12 HOURS OF MOTION.
THE GLOBAL MODELS ARE IN GOOD AGREEMENT ABOUT A GRADUAL TURN TOWARD
THE NORTHWEST TO NORTH-NORTHWEST OVER THE NEXT 5 DAYS.  THE
HURRICANE IS FORECAST TO MOVE AROUND THE PERIPHERY OF A DEEP-LAYER
ANTICYCLONE CENTERED SOUTH OF NOVA SCOTIA.  AN APPROACHING
SHORT-WAVE TROUGH MOVING ACROSS THE EASTERN UNITED STATES IS
FORECAST TO BYPASS ISABEL ON ABOUT DAY 3...BUT THE NEXT SHORT-WAVE
TROUGH SHOULD PICK UP THE HURRICANE BY ABOUT DAY 5.  THE OFFICIAL
FORECAST TRACK IS ADJUSTED SLIGHTLY TO THE EAST OF THE PREVIOUS
ADVISORY BUT IS STILL CLOSE TO THE WESTERN-MOST GUIDANCE WHICH IS
THE GFS MODEL.  THE OFFICIAL TRACK FORECAST SHOWS A DECREASE IN
FORWARD SPEED FOR 3 DAYS FOLLOWED BY AN INCREASE IN FORWARD SPEED
ON DAY 4 AND 5.  NOTE THAT THE 5 DAY FORECAST POSITION IS RATHER
CLOSE TO THE MID-ATLANTIC U.S. COAST.
 
FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0300Z 23.0N  63.7W   140 KT
 12HR VT     14/1200Z 23.7N  65.4W   140 KT
 24HR VT     15/0000Z 24.5N  67.3W   135 KT
 36HR VT     15/1200Z 25.2N  68.7W   130 KT
 48HR VT     16/0000Z 25.9N  69.8W   125 KT
 72HR VT     17/0000Z 28.0N  71.6W   120 KT
 96HR VT     18/0000Z 31.6N  73.4W   110 KT
120HR VT     19/0000Z 36.5N  75.0W   100 KT
 
 
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