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TROPICAL STORM ISAAC DISCUSSION NUMBER   9
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT SAT SEP 23 2000
 
THE INITIAL MOTION ESTIMATE REMAINS 280/10 ALTHOUGH THE POSITION WAS
SHIFTED A LITTLE NORTHWARD BASED ON EARLY VISIBLE IMAGERY.  ALL OF
THE MODELS SHOW A SLOW MOTION VARYING FROM WESTWARD TO NORTHWESTWARD
THROUGH 72 HOURS.  THIS SLOW MOTION IS THE RESULT OF A CUT-OFF UPPER
LOW LOCATED NORTHWEST OF ISAAC AND MOVING SLOWLY.  THE OFFICIAL
TRACK FORECAST IS SHIFTED SLIGHTLY TO THE RIGHT OF THE PREVIOUS
ADVISORY...BUT IS STILL A LITTLE LEFT OF THE MODEL CONSENSUS.

SATELLITE INTENSITY ESTIMATES ARE 4.0/4.0/3.5 FROM TAFB/SAB/KGWC
RESPECTIVELY...SO ISAAC IS NEAR HURRICANE STRENGTH BASED ON THE
DVORAK TECHNIQUE WITH A NICE CENTRAL DENSE OVERCAST FEATURE.  ONE
CAN ALMOST IMAGINE THE HINT OF AN INTERLOCKING BANDING EYE FEATURE
ON THE LATEST VISIBLE IMAGERY AND A 0759Z SSM/I PASS SHOWS A HOLE IN
THE CONVECTION NEAR WHERE THE CENTER IS ESTIMATED TO BE.  SINCE
UPGRADING TO A HURRICANE IS SOMEWHAT IRREVOCABLE...I WILL
CONSERVATIVELY INCREASE THE INITIAL WIND SPEED TO 60 KNOTS AT THIS
TIME AND PROBABLY UPGRADE TO A HURRICANE ON THE NEXT ADVISORY.  THE
PREVIOUS DICUSSION DESCRIBED A SCENARIO OF AN UPPER TROUGH
DEVELOPING OVER ISAAC...BUT THE SHIPS MODEL DOES NOT SHOW ANY STRONG
VERTICAL SHEAR AFFECTING THE INTENSITY FORECAST.  SO THE FORECAST IS
FOR STRENGTHENING TO 80 KNOTS AS IN THE PREVIOUS ADVISORY.
 
FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     23/1500Z 14.4N  33.7W    60 KTS
12HR VT     24/0000Z 14.7N  35.3W    65 KTS
24HR VT     24/1200Z 15.1N  37.3W    75 KTS
36HR VT     25/0000Z 15.5N  39.0W    80 KTS
48HR VT     25/1200Z 15.8N  40.7W    80 KTS
72HR VT     26/1200Z 16.5N  44.0W    80 KTS
  
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