Show Selection: |
#461805 (Received by flhurricane at: 10:56 AM 25.Sep.2011) TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 1100 AM AST SUN SEP 25 2011 OPHELIA IS EXPERIENCING SOUTHWESTERLY VERTICAL SHEAR OF 25-30 KT... WHICH HAS DISPLACED MOST OF THE DEEP CONVECTION WELL TO THE NORTHEAST AND EAST OF THE ALLEGED LOW-LEVEL CENTER. HOWEVER...SOME CONVECTION HAS RECENTLY BEGUN TO DEVELOP CLOSER TO THE CENTER OF THE CYCLONE. THE INITIAL INTENSITY IS BEING MAINTAINED AT 35 KT BASED ON AN EARLIER ASCAT PASS AT 0410Z THAT INDICATED A LARGE AREA OF 35-40 KT WINDS WINDS BETWEEN 150-225 NMI EAST OF THE CENTER IN A BAND OF DEEP CONVECTION. GIVEN THAT THAT BAND OF CONVECTION HAS PERSISTED SINCE THE ASCAT PASS...IT IS ASSUMED THAT AT LEAST 35-KT WINDS STILL EXIST IN THAT RAINBAND. THE INITIAL MOTION ESTIMATE IS 280/08 KT OVER THE PAST 12 HOURS. OPHELIA HAS ACTUALLY MADE A SHARP JOG TO THE WEST OR EVEN SOUTH OF DUE WEST OVER THE PAST 6 HOURS. THIS IS DUE TO THE VERTICAL CIRCULATION BECOMING MORE SHALLOW AS A RESULT OF THE LOSS OF INNER CORE CONVECTION. HOWEVER...THE SHIPS MODEL IS FORECASTING THE CURRENT STRONG SOUTHWESTERLY SHEAR TO ABATE TO AROUND 15-20 KT DURING THE NEXT 6-48 HOURS...WHICH IS EXPECTED TO ALLOW MORE CONVECTION TO REDEVELOP NEAR THE CENTER AND CREATE A MORE VERTICALLY DEEP CIRCULATION. AS A RESULT...OPHELIA SHOULD GRADUALLY TURN TOWARD THE NORTHWEST OVER THE NEXT COUPLE OF DAYS AS AN EASTWARD-MOVING UPPER-LEVEL TROUGH ERODES THE RIDGE TO THE NORTH OF THE CYCLONE. ALTHOUGH THE ECMWF DISSIPATES THE CURRENT LOW-LEVEL CIRCULATION AND SPINS UP ANOTHER CENTER TO THE EAST OF OPHELIA... THERE IS MUCH LESS SPREAD IN THE MODEL GUIDANCE COMPARED TO 24 HOURS AGO. THE ECMWF SOLUTION IS BEING DISCOUNTED DUE TO VERY HIGH SURFACE PRESSURES IN THE NORTHEAST QUADRANT OF THE OPHELIA CIRCULATION...AND THE OFFICIAL FORECAST TRACK LIES A LITTLE WEST OF THE PREVIOUS TRACK AND IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. AS MENTIONED PREVIOUSLY...THE VERTICAL SHEAR IS FORECAST TO DECREASE TO NEARLY HALF ITS CURRENT VALUE DURING THE NEXT 48 HOURS OR SO... WHICH SHOULD ALLOW FOR SOME DEEP CONVECTION TO REDEVELOP NEAR THE CENTER. THE RESULT SHOULD BE AT LEAST A MAINTENANCE OF THE CURRENT INTENSITY. ALTHOUGH THE VERTICAL SHEAR IS EXPECTED TO INCREASE AGAIN BY 72 HOURS AND BEYOND...SOME FAVORABLE UPPER-LEVEL DYNAMICS MAY ALSO COME INTO PLAY...WHICH COULD INDUCE SOME MODEST STRENGTHENING AS INDICATED BY ALL OF THE GLOBAL MODELS. THE NHC INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND REMAINS ABOVE THE SHIPS/LGEM MODELS AND THE CONSENSUS MODEL...ICON. HOWEVER...IF DEEP CONVECTION DOES NOT REDEVELOP SOON NEAR THE ALLEGED CENTER...THE SYSTEM COULD DEGENERATE INTO JUST AN OPEN WAVE BY THIS AFTERNOON. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 18.3N 60.4W 35 KT 40 MPH 12H 26/0000Z 18.8N 61.5W 35 KT 40 MPH 24H 26/1200Z 19.6N 62.8W 35 KT 40 MPH 36H 27/0000Z 20.6N 64.1W 35 KT 40 MPH 48H 27/1200Z 21.4N 65.0W 35 KT 40 MPH 72H 28/1200Z 22.9N 66.0W 40 KT 45 MPH 96H 29/1200Z 25.0N 67.0W 45 KT 50 MPH 120H 30/1200Z 27.5N 67.5W 45 KT 50 MPH $$ FORECASTER STEWART |