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TROPICAL STORM ISAAC DISCUSSION NUMBER   5
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT FRI SEP 22 2000
 
ALTHOUGH DEEP CONVECTION IS NOT ABUNDANT...ISAAC CONTINUES TO LOOK
WELL ORGANIZED THIS MORNING ON SATELLITE IMAGERY.  SATELLITE
INTENSITY ESTIMATES RANGE FROM 35 KT FROM KGWC TO 45 KT FROM TAFB
AND SAB.  A QUIKSCAT PASS THIS MORNING SUGGESTS THAT THE LOWER OF
THESE MAY BE CLOSER TO THE TRUTH.  THE OFFICIAL INTENSITY IS HELD
UNCHANGED.  THE OUTFLOW PATTERN IS IMPROVING AND STRENGTHENING OVER
THE NEXT DAY OR TWO IS EXPECTED.  BEYOND THAT...A LARGE UPPER TROUGH
NEAR 55W WILL HAVE TO GET OUT OF THE WAY...WHICH IS FORECAST BY THE
GLOBAL MODELS...OR THE SHEAR OVER ISAAC WILL INCREASE.  THE
INTENSITY FORECAST IS A LITTLE LESS AGGRESSIVE THAN THE SHIPS MODEL
GUIDANCE PENDING SOME EVIDENCE THAT THE TROUGH IS RETROGRADING.

ISAAC IS EMBEDDED IN THE EASTERLIES TO THE SOUTH OF A MID-
TROPOSPHERIC RIDGE.  THIS RIDGE IS FORECAST TO MAINTAIN ITSELF AND
MOVE WESTWARD WITH THE CYCLONE OVER THE NEXT THREE DAYS.  THE MODEL
GUIDANCE RESPONDS TO THIS WITH A STEADY WEST-NORTHWESTWARD TRACK
THROUGH THE FORECAST PERIOD.  THE OFFICIAL FORECAST IS SIMILAR TO
BUT SLIGHTLY SLOWER THAN THE PREVIOUS ADVISORY...AND IS BETWEEN THE
GFDL AND UKMET.  
 
FORECASTER FRANKLIN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     22/1500Z 13.4N  29.4W    45 KTS
12HR VT     23/0000Z 13.9N  31.6W    55 KTS
24HR VT     23/1200Z 14.5N  34.3W    65 KTS
36HR VT     24/0000Z 14.8N  36.8W    70 KTS
48HR VT     24/1200Z 15.2N  39.0W    75 KTS
72HR VT     25/1200Z 16.0N  43.5W    80 KTS
 
 
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