ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IVAN DISCUSSION NUMBER 6 NATIONAL WEATHER SERVICE MIAMI FL 5 PM EDT MON SEP 21 1998 IVAN CONTINUES TO BE SHEARED FROM THE WEST-SOUTHWEST BUT APPLICATION OF THE DVORAK TECHNIQUE...WHICH ALLOWS FOR THAT PATTERN...SUGGESTS THAT THE SYSTEM HAS STRENGTHENED A LITTLE. MAXIMUM WINDS ARE ESTIMATED TO BE 40 KT. THE HEADING APPEARS TO HAVE EASED OVER TO 320/10 KT. MOST OF THE GUIDANCE SHOWS A CONTINUATION OF THAT TRACK THROUGH 48 HOURS. AFTER THAT TIME...THE TRACKS DIVERGE WITH HEADINGS FROM WNW TO NE SHOWN. THE ENTIRE RANGE IS POSSIBLE DEPENDING ON WHETHER THE UPPER TROUGH AHEAD OF IVAN DEVELOPS INTO A CLOSED LOW OR REMAINS AN ELONGATED BUT OPEN FEATURE. SLIGHT ADDITIONAL STRENGTHENING IS FORECAST. RAPPAPORT FORECAST POSITIONS AND MAX WINDS INITIAL 21/2100Z 19.3N 36.2W 40 KTS 12HR VT 22/0600Z 20.4N 37.3W 40 KTS 24HR VT 22/1800Z 21.9N 38.8W 40 KTS 36HR VT 23/0600Z 23.6N 40.3W 45 KTS 48HR VT 23/1800Z 25.2N 41.8W 45 KTS 72HR VT 24/1800Z 29.0N 44.5W 50 KTS NNNN