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| #109022 (Received by flhurricane at: 4:40 AM 06.Sep.2006) TCDAT1 TROPICAL STORM FLORENCE DISCUSSION NUMBER 11 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062006 500 AM EDT WED SEP 06 2006 A SIGNIFICANT BURST OF DEEP CONVECTION OCCURRED NORTHEAST OF THE ESTIMATED CENTER DURING THE OVERNIGHT HOURS. HOWEVER...SINCE THE LOW LEVEL CIRCULATION REMAINS BOTH ELONGATED AND DISPLACED TO THE SOUTHWEST OF THE STRONGEST ACTIVITY...THIS FLARE UP DOES NOT NECESSARILY INDICATE IMPROVED ORGANIZATION OR AN INCREASE IN INTENSITY. INDEED...DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB ARE UNCHANGED AT 40 KT AND A RECENT UW-CIMSS AMSU INTENSITY ESTIMATE WAS 42 KT. BASED ON THIS DATA...THE INITIAL INTENSITY REMAINS 40 KT. WATER VAPOR IMAGERY SHOWS THAT THE TROUGH TO THE NORTHWEST OF FLORENCE IS BEGINNING TO FRACTURE CAUSING THE FORMATION OF AN UPPER LOW. GLOBAL MODELS INDICATE THIS UPPER LOW WILL BEGIN TO RETROGRADE OVER THE NEXT DAY OR SO CAUSING A GRADUAL REDUCTION IN VERTICAL SHEAR AND A MORE FAVORABLE ENVIRONMENT FOR STRENGTHENING. HOWEVER...THIS EXPECTED EVOLUTION IS STRONGLY DEPENDENT ON THE PHASING OF THE UPPER LOW AND THE CYCLONE. SHOULD FLORENCE GET TOO CLOSE TO THE UPPER LOW...VERTICAL SHEAR WOULD LIMIT THE POTENTIAL FOR DEVELOPMENT. ACCORDINGLY...THE INTENSITY FORECAST REMAINS RATHER TRICKY AND A FAIR AMOUNT OF UNCERTAINTY EXISTS. THE OFFICIAL FORECAST ASSUMES THE VERTICAL SHEAR WILL RELAX IN A DAY OR SO ALLOWING GRADUAL STRENGTHENING IN LINE WITH AVAILABLE GUIDANCE. GIVEN THE RECENT INCREASE IN DEEP CONVECTION...THE CENTER OF FLORENCE CONTINUES TO JUMP AROUND A BIT WITH THE CURRENT POSITION INDICATING SOME RELOCATION TO THE NORTH. THE INITIAL MOTION IS THUS BASED ON A LONGER TERM AVERAGE YIELDING 300/11. THE TRACK FORECAST REASONING REMAINS UNCHANGED AS GLOBAL MODELS ARE IN EXCELLENT AGREEMENT ON THE EASTWARD MIGRATION OF A MID-LEVEL ANTICYCLONE NORTH OF FLORENCE. GUIDANCE IS TIGHTLY CLUSTERED ABOUT A GENERAL WEST-NORTHWEST HEADING OVER THE NEXT 2-3 DAYS. THEREAFTER...A GRADUAL TURN MORE NORTHWARD IS EXPECTED AS THE CYCLONE REACHES THE WESTERN PERIPHERY OF THE ANTICYCLONE. UNFORTUNATELY...THE GLOBALS CONTINUE TO SHOW DISCREPANCIES IN THE EVOLUTION OF AN UPSTREAM SHORT-WAVE TROUGH MOVING THROUGH THE EASTERN UNITED STATES THIS WEEKEND. THIS RESULTS IN DIFFERENCES AMONG THE MODELS IN THE DEGREE...TIMING...AND LOCATION OF THE AFOREMENTIONED NORTHWARD TURN. THE MOST NOTABLE SHIFT IN GUIDANCE FOR THIS PACKAGE IS THE UKMET AND NOGAPS MODELS...BOTH OF WHICH HAVE SHIFTED A LITTLE TO NORTH EARLY IN THE FORECAST AND A LITTLE EAST LATE. GIVEN THE APPARENT NORTHWARD REFORMATION OF THE CENTER INITIALLY...THIS SHIFT APPEARS REASONABLE AND THE OFFICIAL FORECAST FOLLOWS SUIT. THE NEW FORECAST TRACK IS STILL ON THE LEFT SIDE OF GUIDANCE ENVELOP. FORECAST POSITIONS AND MAX WINDS INITIAL 06/0900Z 18.4N 50.2W 40 KT 12HR VT 06/1800Z 19.2N 51.6W 45 KT 24HR VT 07/0600Z 20.3N 53.4W 55 KT 36HR VT 07/1800Z 21.4N 55.5W 60 KT 48HR VT 08/0600Z 22.4N 57.8W 65 KT 72HR VT 09/0600Z 24.4N 62.6W 75 KT 96HR VT 10/0600Z 27.0N 66.5W 85 KT 120HR VT 11/0600Z 29.5N 68.0W 95 KT $$ FORECASTER RHOME/BEVEN |
