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TROPICAL STORM IVAN DISCUSSION NUMBER  12
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT WED SEP 23 1998
 
THE INITIAL INTENSITY WILL REMAIN AT 45 KNOTS BASED UPON DVORAK
CLASSIFICATIONS. THE SYSTEM CONTINUES TO UNDERGO SHEARING FROM THE
UPPER-LEVEL TROUGH TO THE WEST.  THE INTENSITY WILL BE HELD AT 45
KNOTS THROUGH 72 HOURS AS IN THE PREVIOUS PACKAGE. THE SYSTEM MAY
BECOME EXTRA-TROPICAL BEFORE THE END OF THE PERIOD.
 
THE INITIAL MOTION ESTIMATE IS NOW 335/13 KNOTS.  THE PRIMARY
STEERING MECHANISM FOR THIS TROPICAL CYCLONE WILL BE THE TROUGH
TO THE WEST OF IVAN.  MOST OF THE 00Z TRACK MODELS SHOW A
NORTH-NORTHWEST OR NORTH MOTION THROUGH 36 HOURS WITH A TURN TOWARD
THE NORTHEAST.  HOWEVER...BECAUSE OF THE DIFFERENCES IN THE FORWARD
SPEEDS OF THE VARIOUS TRACK MODELS THE TURN TOWARD THE NORTHEAST
OCCURS AT DIFFERENT LATITUDES RESULTING IN A DIVERGENT TRACK SUITE. 
THE OFFICIAL TRACK FORECAST FOLLOWS THIS BASIC SCENARIO AND IS
SIMILAR THE PREVIOUS PACKAGE.  
 
JARVINEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     23/0900Z 27.3N  38.1W    45 KTS
12HR VT     23/1800Z 29.2N  38.9W    45 KTS
24HR VT     24/0600Z 31.4N  39.7W    45 KTS
36HR VT     24/1800Z 33.5N  40.1W    45 KTS
48HR VT     25/0600Z 35.4N  39.9W    45 KTS
72HR VT     26/0600Z 38.9N  38.4W    45 KTS
 
 
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