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| #7514 (Received by flhurricane at: 10:39 PM 04.Sep.2004) TCDAT4 TROPICAL STORM IVAN DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT SAT SEP 04 2004 IVAN CONTINUES TO BECOME BETTER ORGANIZED...WITH A CURVED COLD CONVECTIVE BAND TO THE EAST OF A WARM SPOT THAT IS NOT YET DESERVING OF BEING CALLED AN EYE. SATELLITE INTENSITY ESTIMATES ARE 77 KT FROM AFWA AND 65 KT FROM TAFB AND SAB. HOWEVER...AN SSM/I OVERPASS AT 0005Z DID NOT SHOW AN EYE OR EVEN THAT GOOD OF CONVECTIVE BANDING. THEREFORE...THE SYSTEM WILL REMAIN A TROPICAL STORM AT THIS TIME WITH AN INITIAL INTENSITY OF 60 KT. THE INITIAL MOTION IS 275/16. IVAN REMAINS ON THE SOUTH SIDE OF A STRONG SUBTROPICAL RIDGE...AND THIS SHOULD LIKELY CONTINUE FOR THE NEXT 3-4 DAYS. BY DAY 5...THE CYCLONE WILL BE NEARING A FORECAST WEAKNESS IN THE RIDGE. THIS PATTERN SHOULD ALLOW A GENERALLY WEST- NORTHWESTWARD MOTION FOR THE NEXT 3-4 DAYS...FOLLOWED BY A GRADUAL MORE NORTHERLY TURN. TRACK GUIDANCE IS UNUSUALLY WELL CLUSTERED EVEN OUT TO DAY FIVE...CALLING FOR IVAN TO MOVE WEST-NORTHWESTWARD THROUGH THE CENTRAL LESSER ANTILLES IN ABOUT 72 HR AND THEN PASS OVER HISPANIOLA BETWEEN 96-120 HR. THE NEW FORECAST TRACK FOLLOWS THE MIDDLE OF THIS GUIDANCE SUITE AND IS BASICALLY AN UPDATE OF THE PREVIOUS PACKAGE. LARGE-SCALE GUIDANCE PREDICTS LIGHT VERTICAL SHEAR FOR THE NEXT 3-4 DAYS...SO THERE IS NO OBVIOUS REASON WHY IVAN SHOULD NOT GRADUALLY INTENSIFY. THE INTENSITY FORECAST FOLLOWS THIS PHILOSOPHY. WITH THE FORECAST TRACK TAKING THE STORM OVER HISPANIOLA BETWEEN 96-120 HR...THE FORECAST INTENSITY IS CONSIDERABLY REDUCED. THERE IS ALSO SOME UNCERTAINTY OF WHETHER THE SHEAR WILL REMAIN FAVORABLE AFTER 96 HR...AS THE GFS AND NOGAPS DEVELOP AN UPPER-LEVEL TROUGH OVER THE BAHAMAS BY 120 HR. AS NOTED EARLIER...BECAUSE OF THE TYPICAL TRACK FORECAST ERRORS AT 5 DAYS...THE CENTER COULD EASILY PASS SOUTH...OR NORTH...OF THE ISLAND OF HISPANIOLA. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 05/0300Z 9.4N 42.2W 60 KT 12HR VT 05/1200Z 9.8N 44.7W 65 KT 24HR VT 06/0000Z 10.7N 48.2W 70 KT 36HR VT 06/1200Z 11.8N 51.5W 75 KT 48HR VT 07/0000Z 12.7N 55.1W 80 KT 72HR VT 08/0000Z 14.5N 61.5W 90 KT 96HR VT 09/0000Z 16.5N 67.0W 100 KT 120HR VT 10/0000Z 20.0N 72.0W 65 KT |
