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| #7741 (Received by flhurricane at: 4:41 PM 09.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 30 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT THU SEP 09 2004 BOTH NOAA AND AIR FORCE RECONNAISSANCE PLANES HAVE BEEN IN THE EYE OF IVAN DURING THE PAST FEW HOURS. MINIMUM PRESSURE REMAINS AT ABOUT 921 MB BUT MAXIMUM FLIGHT LEVEL WINDS HAVE DECREASED TO 144 KNOTS. THIS SUGGESTS THAT INITIAL INTENSITY CAN BE LOWERED TO 130 KNOTS AT THIS TIME. THERE WERE SOME INDICATIONS FROM MICROWAVE DATA AND NOW CONFIRMED WITH THE PLANE THAT IVAN HAS A DOUBLE EYEWALL STRUCTURE. THIS MAY EXPLAIN THE RECENT SLIGHT WEAKENING. THE HURRICANE WILL PROBABLY FLUCTUATE BETWEEN CAT 4 AND 5 WHILE MOVING THROUGH AN AREA OF LOW SHEAR AND HIGH OCEANIC HEAT CONTENT BEFORE REACHING CUBA. THEREAFTER...THE EFFECTS OF LAND AND INCREASING SHEAR WILL CAUSE A GRADUAL WEAKENING. IVAN CONTINUES TO MOVE TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 13 KNOTS. THIS GENERAL MOTION WITH A GRADUAL DECREASE IN FORWARD SPEED IS EXPECTED DURING THE NEXT 2 TO 3 DAYS. AS MENTIONED IN THE PREVIOUS DISCUSSION...THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE FORECAST BECAUSE THE HURRICANE WILL BE STEERED BY THE FLOW SURROUNDING A WELL-ESTABLISHED SUBTROPICAL RIDGE. ALL MODELS ARE HIGHLY CLUSTERED DURING THIS PERIOD...BRINGING THE HURRICANE NEAR OR OVER JAMAICA...THE CAYMAN ISLANDS AND WESTERN CUBA WITH A DECREASE IN FORWARD SPEED. THEREAFTER...THE TRACK CONTINUES TO BE UNCERTAIN SINCE STEERING CURRENTS ARE FORECAST TO WEAKEN AND MODELS DIVERGE. HOWEVER...MODELS FROM 12Z ARE IN SLIGHTLY BETTER AGREEMENT THAN IN EARLIER RUNS...AND IN GENERAL HAVE SHIFTED A LITTLE BIT WESTWARD. THE OFFICIAL FORECAST ALSO SHOWS A SLIGHT WESTWARD SHIFT. THE WIND RADII WERE ADJUSTED BASED ON THE STEPPED FREQUENCY MICROWAVE RADIOMETER DATA ONBOARD THE NOAA P3 PLANE CURRENTLY INVESTIGATING IVAN. FORECASTER AVILA FORECAST POSITIONS AND MAX WINDS INITIAL 09/2100Z 15.0N 72.5W 130 KT 12HR VT 10/0600Z 16.1N 74.2W 130 KT 24HR VT 10/1800Z 17.5N 76.2W 135 KT 36HR VT 11/0600Z 18.8N 78.0W 130 KT 48HR VT 11/1800Z 19.7N 79.3W 140 KT 72HR VT 12/1800Z 21.5N 81.5W 140 KT 96HR VT 13/1800Z 25.0N 83.0W 115 KT 120HR VT 14/1800Z 28.0N 83.5W 100 KT |
