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| #7228 (Received by flhurricane at: 5:06 AM 03.Sep.2004) TCDAT1 HURRICANE FRANCES DISCUSSION NUMBER 38 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT FRI SEP 03 2004 FRANCES CONTINUES TO SLOWLY WEAKEN. WHILE IT CONTINUES TO GENERATE COLD CONVECTIVE TOPS OVER THE CENTER...AIR FORCE RESERVE HURRICANE HUNTER AND BAHAMA RADAR DATA SHOW THAT THE TOPS ARE COMING FROM EYEWALL FRAGMENTS IN THE NORTHEASTERN QUADRANT. THE MINIMUM CENTRAL PRESSURE HAS RISEN TO 954 MB...AND THE MAXIMUM FLIGHT-LEVEL WINDS ON THE LAST MISSION WERE 98 KT. THE INITIAL INTENSITY IS REDUCED TO 105 KT BASED PRIMARILY ON THE CENTRAL PRESSURE AND SATELLITE INTENSITY ESTIMATES...AS THE AIRCRAFT WINDS...INCLUDING DROPSONDES...DO NOT CURRENTLY SUPPORT THIS INTENSITY. THE INITIAL MOTION IS 300/8. FRANCES IS ON THE SOUTHWEST SIDE OF A COMPLEX RIDGE THAT HAS ONE ANTICYCLONE CENTER EAST OF FRANCES AND ANOTHER TO THE NORTH. LARGE-SCALE MODELS FORECAST HEIGHTS TO RISE NORTH OF FRANCES THROUGH 72 HR AS A SHORT WAVE RIDGE MOVES THROUGH THE EASTERN UNITED STATES. AFTER 72 HR...HEIGHTS RISE OVER THE WESTERN ATLANTIC AS A TROUGH DEVELOPS OVER THE CENTRAL UNITED STATES. THIS PATTERN EVOLUTION SHOULD STEER FRANCES WEST- NORTHWESTWARD TO NORTHWESTWARD FOR 24-36 HR...FOLLOWED BY SOME TURN TOWARD THE LEFT AND SLOWER MOTION FROM 36-48 HR...THEN FASTER MOTION TOWARD THE NORTHWEST AND THEN NORTH. NHC TRACK GUIDANCE GENERALLY AGREES WITH THIS SCENARIO...WITH A TIGHT CLUSTERING OF GUIDANCE THROUGH THE FIRST 48 HR AND AND SOME SPREAD BETWEEN A NORTHWESTWARD MOTION AND A NORTHWARD TURN THEREAFTER. THE OFFICIAL FORECAST IS SIMILAR TO...BUT SLOWER THAN THE PREVIOUS PACKAGE IN DEFERENCE TO THE GFS AND GFDL...WHICH SLOW FRANCES TO 4 KT JUST PRIOR TO LANDFALL ON THE FLORIDA PENINSULA. THE FORECAST SLOW FORWARD SPEED WILL PROLONG THE ADVERSE AND HAZARDOUS CONDITIONS ASSOCIATED WITH FRANCES. THE INTENSITY FORECAST IS VERY PROBLEMATIC. ON ONE SIDE...THE HURRICANE WIND FIELD HAS BECOME VERY SPREAD OUT AS THE CENTRAL CORE WEAKENS...AND IT IS OFTEN DIFFICULT FOR THIS TYPE OF SPREAD OUT SYSTEM TO RE-CONSOLIDATE. ALSO...SHEAR ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN NOW SHOW 15-20 KT OF WESTERLY SHEAR ACROSS FRANCES. THE SHIPS MODEL FORECAST THIS SHEAR TO PERSIST UNTIL JUST BEFORE LANDFALL. ON THE OTHER HAND...THE STORM HAS A GOOD CYCLONIC ENVELOPE AND IS STILL GENERATING STRONG CONVECTION. THE INTENSITY FORECAST WILL GO WITH THE SCENARIO THAT FRANCES WILL GRADUALLY RE-CONSOLIDATE BEFORE LANDFALL AND RE-GAIN SOME STRENGTH. AN ALTERNATIVE SCENARIO IS THAT FRANCES DOES NOT RE-INTENSIFY OR PERHAPS WEAKENS MORE AS INDICATED BY THE SHIPS AND GFDL MODELS. THIS PART OF THE FORECAST IS LOW CONFIDENCE. THE 64 AND 50 KT WIND RADII WERE MODIFIED IN THE NW QUADRANT BASED ON AIRCRAFT DATA...WHICH REPORTED A 95 KT FLIGHT-LEVEL WIND 90 NM NORTHWEST OF THE CENTER. AT THIS TIME...CHANGES IN THE WARNINGS AND WATCHES ARE NOT NECESSARY. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 03/0900Z 24.9N 76.0W 105 KT 12HR VT 03/1800Z 25.7N 77.1W 110 KT 24HR VT 04/0600Z 26.4N 78.3W 115 KT 36HR VT 04/1800Z 27.1N 79.5W 120 KT 48HR VT 05/0600Z 27.6N 80.7W 105 KT...INLAND 72HR VT 06/0600Z 29.0N 83.0W 45 KT...OVER GULF OF MEXICO 96HR VT 07/0600Z 32.0N 86.0W 30 KT...INLAND 120HR VT 08/0600Z 35.0N 86.5W 25 KT...INLAND |
