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HURRICANE ISAAC DISCUSSION NUMBER  20
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT TUE SEP 26 2000
 
DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN AT 90 KT...AND I
NOTE IN PASSING THAT THE PREVIOUS ESTIMATE FROM SAB WAS ERRONEOUSLY
REPORTED TO BE 102 KT.   THERE IS NO EYE PRESENT.  THE LAST FEW
SATELLITE IMAGES...AS WELL AS A RECENTLY-RECEIVED MICROWAVE
PASS...INDICATE THAT SHEAR IS BEGINNING TO HAVE A GREATER IMPACT ON
ISAAC.  IN FACT...VISIBLE IMAGERY IN ANOTHER HOUR OR TWO MAY SHOW
THAT THE LOW-LEVEL CENTER IS FARTHER SOUTH AND WEST THAN I HAVE WITH
THIS ADVISORY.  IF SO...THE SYSTEM IS NOT AS STRONG AS INDICATED
HERE.

MODEL GUIDANCE IS IN GOOD AGREEMENT ON A CONTINUED WEST-NORTHWEST
TRACK FOR THE NEXT DAY OR TWO FOLLOWED BY A TURN TO THE NORTHWEST. 
AS THE UPPER TROUGH MOVES INTO THE WESTERN ATLANTIC THE STEERING
GRADIENT SHOULD INCREASE AND RESULT IN A SLIGHTLY FASTER FORWARD
SPEED.  THE OFFICIAL FORECAST IS SLIGHTLY FASTER THAN THE PREVIOUS
ADVISORY IN THE LAST 24 HOURS.

FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     26/0900Z 18.7N  43.0W    90 KTS
12HR VT     26/1800Z 19.3N  44.2W    90 KTS
24HR VT     27/0600Z 20.3N  46.0W    90 KTS
36HR VT     27/1800Z 21.4N  47.9W    90 KTS
48HR VT     28/0600Z 23.0N  50.5W    90 KTS
72HR VT     29/0600Z 27.0N  55.5W    90 KTS
 
 
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