Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  40
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 15 2003
 
THE DEEP CONVECTION HAS CONTINUED TO ERODE ON THE WEST SIDE OF
ISABEL SINCE THE 18Z RECONNAISSANCE AIRCRAFT DATA INDICATED 110
KNOTS...SO THE ADVISORY INITIAL WIND SPEED IS REDUCED 5 KNOTS TO
105 KNOTS.  THE SHIPS MODEL AS WELL AS SEVERAL OF THE GLOBAL MODELS
INDICATE LITTLE CHANGE IN WIND SPEED BEFORE LANDFALL WHICH IS
EXPECTED BETWEEN 48 AND 60 HOURS.  THE SHIPS MODEL DIAGNOSES THE
GFS VERTICAL SHEAR NEAR 30 KNOTS AT 48 HOURS SO IT IS DIFFICULT TO
UNDERSTAND WHY THE GUIDANCE DOES NOT CALL FOR MORE WEAKENING BEFORE
LANDFALL.  PERHAPS IT IS THE PATH OVER THE GULFSTREAM THAT WILL
KEEP THE WIND SPEED UP.  ANYWAY THE OFFICIAL WIND SPEED IS REDUCED
ONLY 5 MORE KNOTS BEFORE LANDFALL TO 100 KNOTS...STILL A CATEGORY
THREE HURRICANE ON THE SAFFIR SIMPSON SCALE.

THE FORECAST TRACK AND SCENARIO IS VERY SIMILAR TO THE PREVIOUS
ADVISORY.  THE INITIAL MOTION ESTIMATE IS 320/06.  THE GUIDANCE IS
TIGHTLY CLUSTERED ABOUT A NORTH-NORTHWESTWARD TRACK AT LESS THAN 10
KNOTS FORWARD SPEED FOR 48 HOURS AS THE HURRICANE MOVES AROUND THE
WEST SIDE OF A DEEP-LAYER MEAN RIDGE WHILE BEING BYPASSED BY A
SHORT-WAVE TROUGH.  A SECOND SHORT-WAVE TROUGH WILL ACCELERATE THE
TRACK NORTH-NORTHWESTWARD WITH THE CENTER INLAND IN 72 HOURS.  

FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/0300Z 26.1N  70.2W   105 KT
 12HR VT     16/1200Z 26.9N  70.8W   105 KT
 24HR VT     17/0000Z 28.4N  71.7W   100 KT
 36HR VT     17/1200Z 29.8N  72.5W   100 KT
 48HR VT     18/0000Z 31.5N  73.7W   100 KT
 72HR VT     19/0000Z 37.2N  77.2W    60 KT...INLAND
 96HR VT     20/0000Z 44.5N  79.5W    40 KT...INLAND...EXTRATROPICAL
120HR VT     21/0000Z 54.0N  78.5W    30 KT...INLAND...EXTRATROPICAL
 
 
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