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| #7776 (Received by flhurricane at: 10:50 PM 09.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 31 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT THU SEP 09 2004 THE LAST REPORT FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATED THAT THE CENTRAL PRESSURE OF IVAN WAS STILL 923 MB...BUT THAT THE MAXIMUM FLIGHT-LEVEL WINDS HAD DECREASED TO NEAR 130 KT. BASED MAINLY ON THE PRESSURE...THE INITIAL INTENSITY REMAINS A POSSIBLY GENEROUS 130 KT FOR THIS PACKAGE. THE AIRCRAFT DATA INDICATE THAT THE OUTER WIND MAXIMA MENTIONED IN THE PREVIOUS ADVISORY WAS CONTRACTING...AND THE LATEST SATELLITE IMAGERY SUGGESTS THAT IVAN MAY BE COMPLETING THE CURRENT CONCENTRIC EYEWALL CYCLE. HOWEVER...THE AIRCRAFT DATA ALSO INDICATES ANOTHER WIND MAXIMA FORMING OVER THE NORTHERN SEMICIRCLE...WHICH MAY BE THE PRECURSOR OF THE NEXT CONCENTRIC EYEWALL CYCLE. THE INITIAL MOTION IS NOW 300/11. THERE IS HIGH CONFIDENCE IN THE FIRST 36-48 HR OF THE FORECAST TRACK...AS THE SUBTROPICAL RIDGE TO THE NORTHEAST OF IVAN SHOULD STEER IT GENERALLY WEST-NORTHWESTWARD. CONFIDENCE DIMINISHES BEYOND THAT TIME AS THE RIDGE WEAKENS DUE TO AN UPPER-LEVEL TROUGH OVER THE EASTERN UNITED STATES AND AN UPPER-LEVEL LOW OVER THE ATLANTIC CURRENTLY NEAR 31N52W. ALL GUIDANCE AGREES ON A TURN TOWARD THE NORTH...WITH DIFFERENCES ON HOW FAR EAST THAT TURN WILL OCCUR. THE GFS WEAKENS THE RIDGE THE MOST AND BRINGS IVAN NORTHWARD THROUGH THE FLORIDA PENINSULA. THE UKMET AND NOGAPS KEEP MORE RIDGING NORTH OF IVAN AND THUS KEEP A MORE NORTH-NORTHWESTWARD MOTION. THE NOGAPS AND GFS HAVE BOTH SHIFTED A LITTLE TO THE LEFT...WHILE THE GFDL HAS SHIFTED TO THE RIGHT. THE OFFICIAL TRACK FORECAST IS BASICALLY AN UPDATE ON THE PREVIOUS PACKAGE...SHIFTING SLIGHTLY TO THE RIGHT AFTER 72 HR TO BRING IT IN BEST AGREEMENT WITH THE GUNS AND CONU CONSENSUS MODELS. THE INTENSITY FORECAST IS PROBLEMATIC. THE BIGGEST CONTROLLING FACTOR THROUGH THE FIRST 72 HR IS LIKELY TO BE CONCENTRIC EYEWALL CYCLES. THE INTENSITY FORECAST ASSUMES THAT IVAN WILL COMPLETE THE CURRENT CYCLE BEFORE IT REACHES JAMAICA AND THUS INTENSIFY BEFORE HITTING THE ISLAND. FURTHER INTENSIFICATION IS LIKELY OVER THE WARM WATER BETWEEN JAMAICA AND CUBA IF THE STORM STRUCTURE REMAINS GOOD. ON THE OTHER HAND...THE GFS...NOGAPS...AND SHIPS ALL FORECAST SIGNIFICANT SHEAR TO DEVELOP ACROSS IVAN STARTING IN ABOUT 48 HR...WHICH COULD SLOW OR STOP DEVELOPMENT IN SPITE OF THE WARM WATER. GIVEN THE CURRENT IMPRESSIVE OUTFLOW PATTERN...48 HR MIGHT BE TOO SOON. THE INTENSITY FORECAST WILL DELAY THE ONSET OF SIGNIFICANT SHEAR UNTIL 72 HR AND HOLDS THE INTENSITY UP ACCORDINGLY. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 10/0300Z 15.5N 73.3W 130 KT 12HR VT 10/1200Z 16.5N 74.8W 130 KT 24HR VT 11/0000Z 17.7N 76.6W 135 KT 36HR VT 11/1200Z 18.9N 78.3W 130 KT 48HR VT 12/0000Z 19.9N 79.6W 140 KT 72HR VT 13/0000Z 22.0N 81.5W 140 KT 96HR VT 14/0000Z 25.5N 82.5W 120 KT 120HR VT 15/0000Z 29.5N 83.0W 95 KT...INLAND |
