ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IVAN DISCUSSION NUMBER 4 NATIONAL WEATHER SERVICE MIAMI FL 5 AM EDT MON SEP 21 1998 A SHEARING PATTERN CONTINUES TO INHIBIT THE STRENGTHENING OF IVAN. DEEP CONVECTION CONTINUES NEAR THE CENTER...ALTHOUGH IT IS RAGGED IN APPEARANCE AND IS REFLECTED IN THE T-NUMBERS WHICH ARE 2.0/2.5/2.0...SO THAT IVAN IS A BORDER LINE TROPICAL STORM. THE INITIAL ESTIMATE REMAINS AT 35 KNOTS...ALTHOUGH THE FORECAST IS FOR WEAKENING TO DEPRESSION INTENSITY IN 24 HOURS IN LINE WITH FORECAST OF INCREASING VERTICAL SHEAR. THE SYSTEM IS FORECAST TO RETURN BACK TO TROPICAL STORM STATUS IN 72 HOURS AS THE SHEAR IS REDUCED. BOTH THE SHIPS AND THE GFDL INTENSITY FORECASTS ALSO SUPPORT THIS. INITIAL MOTION ESTIMATE REMAINS AT 295/12. THE MODEL TRACK FORECASTS ARE IN BETTER AGREEMENT THAN IN PREVIOUS PACKAGE AND TAKE THE SYSTEM NORTHWEST...BUT WITH VARYING SPEEDS. THE OFFICIAL FORECAST REFLECTS NHC AND HPC INPUT AND IS SOMEWHAT SIMILAR TO THE PREVIOUS PACKAGE. JARVINEN FORECAST POSITIONS AND MAX WINDS INITIAL 21/0900Z 17.4N 35.3W 35 KTS 12HR VT 21/1800Z 18.0N 36.0W 35 KTS 24HR VT 22/0600Z 19.1N 38.0W 30 KTS 36HR VT 22/1800Z 20.5N 39.5W 30 KTS 48HR VT 23/0600Z 22.0N 41.5W 30 KTS 72HR VT 24/0600Z 25.0N 45.0W 35 KTS NNNN