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| #461394 (Received by flhurricane at: 4:59 PM 23.Sep.2011) TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 500 PM AST FRI SEP 23 2011 DEEP CONVECTION HAS REDEVELOPED NEAR AND OVER THE LOW-LEVEL CENTER DURING THE PAST 6 HOURS...AND REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INDICATE THE INTENSITY HAS INCREASED TO 50 KT BASED ON FLIGHT-LEVEL WINDS OF 60 KT AND BELIEVABLE SFMR SURFACE WINDS OF 50-51 KT. THE INITIAL MOTION IS 285/13...AFTER ONCE AGAIN HAVING TO SMOOTH THROUGH ALL OF THE WIGGLES AND WOBBLES IN THE TRACK. THE DEVELOPMENT OF THE DEEP CONVECTION NEAR THE CENTER LIKELY PULLED THE BARELY-CLOSED LOW-LEVEL CIRCULATION CENTER NORTHWESTWARD... WHICH IS BELIEVED TO BE A TEMPORARY MOTION. OTHERWISE...THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK. MOST OF THE MODEL GUIDANCE SHIFTED TO THE RIGHT DUE TO THE MORE NORTHWARD INITIAL POSITION...BUT THE SUBTROPICAL RIDGE TO THE NORTH OF OPHELIA IS FORECAST BY ALL OF THE GLOBAL MODELS TO REMAIN QUITE STRONG...WHICH SHOULD KEEP THE CYCLONE MOVING IN A GENERAL WEST-NORTHWESTWARD MOTION FOR THE NEXT 48 HOURS OR SO. BY 72 HOURS AND BEYOND...THE WESTERN PORTION OF THE RIDGE IS FORECAST TO ERODE AS A MID-/UPPER-LEVEL TROUGH MOVES EASTWARD ACROSS FLORIDA AND THE BAHAMAS. THIS SHOULD CAUSE OPHELIA TO SLOW DOWN AND TURN NORTHWESTWARD BY DAYS 3-4...AND THEN ALLOW FOR A GRADUAL NORTHWARD TURN BY DAY 5. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY TRACK...AND LIES NEAR THE SOUTHERN OR LEFT SIDE OF THE NHC GUIDANCE ENVELOPE. ALTHOUGH THE GFS-BASED SHIPS MODEL IS ASSESSING NEAR 20 KT OF SOUTHWESTERLY SHEAR ACROSS THE CYCLONE...THE UW-CIMSS MID-LEVEL SHEAR ANALYSES INDICATE THE SHEAR IS 15 KT OR LESS. THIS HAS LIKELY ALLOWED THE RECENT RESURGENCE IN INNER CORE CONVECTION. HOWEVER... THIS BRIEF RESPITE IS EXPECTED TO BE SHORT-LIVED AS ALL OF THE GLOBAL MODELS ARE FORECASTING THE VERTICAL SHEAR TO INCREASE TO MORE THAN 25 KT IN 12-18 HOURS. THERE WILL CONTINUE TO BE FLUCTUATIONS IN THE MAGNITUDE OF THE VERTICAL SHEAR FOR THE NEXT 96 HOURS...WHICH WILL RESULT IN THE WAXING AND WANING OF THE CENTRAL DEEP CONVECTION...BUT THE GENERAL TREND SHOULD BE FOR GRADUAL WEAKENING TO OCCUR. HOWEVER...BY DAY 5...SOME SLIGHT STRENGTHENING IS POSSIBLE AS THE SHEAR DECREASES AND OPHELIA MOVES UNDERNEATH OR NEAR A SMALL UPPER-LEVEL ANTICYCLONE. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 15.5N 53.8W 50 KT 60 MPH 12H 24/0600Z 16.3N 55.7W 50 KT 60 MPH 24H 24/1800Z 17.5N 58.0W 45 KT 50 MPH 36H 25/0600Z 18.6N 60.0W 45 KT 50 MPH 48H 25/1800Z 19.7N 61.8W 40 KT 45 MPH 72H 26/1800Z 21.8N 64.9W 40 KT 45 MPH 96H 27/1800Z 24.0N 66.6W 40 KT 45 MPH 120H 28/1800Z 26.5N 67.5W 45 KT 50 MPH $$ FORECASTER STEWART |
