ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IVAN DISCUSSION NUMBER 9 NATIONAL WEATHER SERVICE MIAMI FL 11 AM EDT TUE SEP 22 1998 IVAN HAS ACCELERATED TO ABOUT 20 KT DURING THE PAST 6 HOURS...WITH A 12-HOUR MOTION ESTIMATED AT 355/14 KT. THE INCREASE IN FORWARD SPEED IS LIKELY THE RESULT OF IVAN BEING CAUGHT IN THE CIRCULATION AROUND THE UPPER-LOW CUTTING OFF TO THE SSW. THERE ARE TWO PRIMARY POSSIBILITIES FOR THE FUTURE TRACK. AS THE INTERACTION WITH THE UPPER LOW ENDS...SOME DECELERATION AND A TURN MORE TOWARD THE NW ARE POSSIBLE. THE GFDL...UKMET...NOGAPS...AND BAMS ALL SHOW THIS. MEANWHILE...THE OTHER GUIDANCE SHOWS A CONTINUING RECURVATURE. THIS OFFICIAL FORECAST LEANS BACK A LITTLE TOWARD THE FORMER OPTION AS...AT THE MOMENT..THIS SEEMS TO BE MOST CONSISTENT WITH THE CURRENT LARGE-SCALE PATTERN AND EXPECTED EVOLUTION. VISIBLE SATELLITE PICTURES REVEAL THE CENTER MOSTLY EXPOSED TO THE S OR SSE OF DEEP CONVECTION. IN THIS SHEARING ENVIRONMENT...LITTLE CHANGE WILL BE SHOWN FOR THE WIND SPEED. RAPPAPORT FORECAST POSITIONS AND MAX WINDS INITIAL 22/1500Z 23.6N 36.3W 45 KTS 12HR VT 23/0000Z 25.6N 37.1W 45 KTS 24HR VT 23/1200Z 26.8N 37.7W 45 KTS 36HR VT 24/0000Z 28.4N 37.9W 45 KTS 48HR VT 24/1200Z 30.2N 37.9W 50 KTS 72HR VT 25/1200Z 33.0N 37.0W 50 KTS NNNN