ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IVAN DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SAT SEP 04 2004 THE SATELLITE SIGNATURE ASSOCIATED WITH IVAN HAS IMPROVED OVERNIGHT AND DVORAK INTENSITY ESTIMATES ARE 45 KT AND 55 KT FROM TAFB AND SAB RESPECTIVELY. THE OFFICIAL INTENSITY SPLITS THE DIFFERENCE AT 50 KT. UNIVERSITY OF WISCONSIN-CIMSS SATELLITE ANALYSIS CONTINUES TO SHOW MODERATE VERTICAL SHEAR OVER IVAN. HOWEVER...SATELLITE IMAGERY INDICATES THAT THE SHEAR IS NOT DISRUPTING UPPER-LEVEL OUTFLOW WHICH IS UNOBSTRUCTED IN ALL QUADRANTS INCLUDING TO THE EAST. IVAN HAS BEEN STEADILY STRENGTHENING AND THE SHEAR IS FORECAST TO DECREASE. THUS...THERE ARE NO APPARENT REASONS WHY IVAN SHOULD NOT CONTINUE STRENGTHENING DURING THE FORECAST PERIOD. THE SHIPS MODEL BRINGS THE WIND SPEED TO NEAR 100 KT IN 120 HOURS WHILE THE GFDL CONTINUES TO FORECAST MORE VIGOROUS STRENGTHENING TO 135 KT. THUS FAR...THE SHIPS HAS BEEN THE BETTER PERFORMER OF THE TWO MODELS AND THE OFFICIAL FORECAST FOLLOWS IT CLOSELY. IVAN APPEARS TO BE MOVING ALONG AS EXPECTED AND THE INITIAL MOTION IS 270/16. THERE HAS BEEN LITTLE CHANGE IN THE OVERALL FORECAST PHILOSOPHY AS THE GLOBAL MODELS CONTINUE TO SHOW A SUBTROPICAL RIDGE BUILDING WESTWARD WITH IVAN. THIS WOULD TEND TO STEER IVAN ON A GENERAL WEST-NORTHWEST MOTION BETWEEN 15-17 KNOTS. BEYOND 72 HOURS...GLOBAL MODELS SHOW IVAN APPROACHING A WEAKNESS IN THE SUBTROPICAL RIDGE WHICH WOULD ALLOW A MORE POLEWARD MOTION AND SLIGHTLY SLOWER SPEED. IT IS INTERESTING TO NOTE THAT THE NOGAPS IS NOW IN MUCH BETTER AGREEMENT WITH THE OTHER DYNAMICAL MODELS AND THE NHC MODEL SUITE IS MORE TIGHTLY CLUSTERED. THE GFS IS SOMEWHAT OF AN OUTLIER AS IT WEAKENS IVAN EAST OF THE LESSER ANTILLES AND THEN MOVES IT MORE WESTWARD. GIVEN THE CURRENT TREND OF INTENSIFICATION...THIS SOLUTION IS HARD TO ACCEPT. ONLY MINOR CHANGES ARE MADE TO THE OFFICIAL FORECAST WHICH ESSENTIALLY FOLLOWS THE MODEL CONSENSUS. ON THIS TRACK..IVAN WOULD AFFECT THE LESSER ANTILLES IN 4 TO 5 DAYS. FORECASTER RHOME/JARVINEN FORECAST POSITIONS AND MAX WINDS INITIAL 04/0900Z 9.0N 37.4W 50 KT 12HR VT 04/1800Z 9.1N 39.8W 55 KT 24HR VT 05/0600Z 9.7N 43.0W 60 KT 36HR VT 05/1800Z 10.5N 46.2W 65 KT 48HR VT 06/0600Z 11.4N 49.4W 75 KT 72HR VT 07/0600Z 13.0N 55.5W 85 KT 96HR VT 08/0600Z 14.5N 61.0W 95 KT 120HR VT 09/0600Z 17.0N 65.6W 100 KT $$ NNNN
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Page last modified: Saturday, 04-Sep-2004 08:52:49 UTC