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#105628 (Received by flhurricane at: 5:00 AM 23.Aug.2006) TCDAT4 TROPICAL STORM DEBBY DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042006 500 AM EDT WED AUG 23 2006 THE SATELLITE APPEARANCE OF DEBBY CONTINUES TO IMPROVE AND A 0331 UTC AQUA MICROWAVE OVERPASS DETECTED A FAIRLY WELL ORGANIZED SYSTEM...WITH WELL DEFINED BANDS AROUND THE CENTER. DVORAK INTENSITY ESTIMATES ARE 45 KT FROM SAB...AND 35 KT FROM TAFB AND AFWA. THEREFORE...THE INITIAL INTENSITY IS INCREASED TO 40 KT. THE INITIAL MOTION ESTIMATE IS 295/14. DEBBY IS CURRENTLY BEING STEERED WEST-NORTHWEST TO NORTHWESTWARD AROUND THE SOUTHWESTERN PERIPHERY OF A MID-TO UPPER-LEVEL RIDGE CENTERED NEAR THE AZORES. THE RELIABLE TRACK MODELS ARE TIGHTLY CLUSTERED...MAINTAINING THIS MOTION THROUGH THE NEXT 48 TO 72 HOURS. AT DAYS 4 AND 5...GLOBAL MODELS DEVELOP A SIGNIFICANT WEAKNESS IN THE RIDGE AS A MID- TO UPPER-LEVEL TROUGH AMPLIFIES OVER THE CENTRAL ATLANTIC. THE TRACK DIFFERENCES SEEN IN THE THE GLOBAL MODELS APPEAR TO BE THE RESULT OF DIFFERENCES IN THE FORECAST STRENGTH OF THE TROPICAL CYCLONE. THE UMKET MODEL DEPICTS A MUCH WEAKER SYSTEM AND IN TURN TRACKS IT MORE WESTWARD...WHILE THE GFS AND GFDL MODELS HAVE A STRONGER CYCLONE WHICH FEELS THE EFFECTS OF THE TROUGH AND TURNS NORTHWARD NEAR THE END OF THE PERIOD. THE NOGAPS TRACK SEEMS UNREASONABLE BECAUSE IT RESULTS FROM AN UNREALISTIC DISSIPATION OF THE LOW-LEVEL CIRCULATION AND REFORMATION OF THE SYSTEM FROM A MID- TO UPPER-LEVEL LOW TO THE WEST. THE OFFICIAL TRACK FORECAST IS VERY CLOSE TO THE PREVIOUS ADVISORY THROUGH 72 HOURS. THEREAFTER... IT HAS BEEN SHIFTED SLIGHTLY TO THE RIGHT IN GENERAL AGREEMENT WITH THE GFS...GFDL...AND THE FSU SUPERENSEMBLE SOLUTIONS. DEBBY WILL BE ENCOUNTERING DRIER MID-LEVEL AIR AND SLIGHTLY COOLER SSTS OVER THE NEXT 36 HOURS OR SO...WHICH SHOULD KEEP INTENSIFICATION SLOW IN THE NEAR TERM. THEREAFTER... THE CYCLONE WILL BE PASSING OVER WARMER SSTS...BUT SHEAR IS FORECAST TO STRENGTHEN WHICH MAKES FOR A DIFFICULT INTENSITY PREDICTION. THE NHC FORECAST BRINGS DEBBY TO HURRICANE STRENGTH IN 4 DAYS...WHICH IS VERY CLOSE TO THE CONSENSUS OF THE GFDL AND SHIPS...BUT IS LEVELED OFF IN DEFERENCE TO THE POSSIBILITY OF INCREASING SHEAR. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0900Z 15.9N 30.1W 40 KT 12HR VT 23/1800Z 16.9N 32.2W 45 KT 24HR VT 24/0600Z 18.2N 35.0W 50 KT 36HR VT 24/1800Z 19.6N 37.9W 50 KT 48HR VT 25/0600Z 21.0N 40.8W 50 KT 72HR VT 26/0600Z 24.0N 46.5W 60 KT 96HR VT 27/0600Z 27.5N 51.0W 65 KT 120HR VT 28/0600Z 30.0N 53.0W 65 KT |