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| #461635 (Received by flhurricane at: 4:44 PM 24.Sep.2011) TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 500 PM AST SAT SEP 24 2011 DURING THE PAST 6 HOURS...CONVECTION HAS WAXED AND WANED...AND THE INNER CORE WIND FIELD HAS BECOME RATHER AMORPHOUS. BOTH NOAA AND AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT HAVE HAD GREAT DIFFICULTY IN TRYING TO IDENTIFY A WELL-DEFINED CIRCULATION CENTER. IN FACT... THE PREVIOUS ALLEGED CENTER THAT WE HAVE BEEN TRACKING FOR THE PAST 24 HOURS NO LONGER EXISTS BASED ON RECON DATA...AND THE LONE VORTEX REPORTED APPEARS TO HAVE DEGENERATED AS WELL. THE INITIAL POSITION IS THE MEAN POSITION OF ALL OF THE PREVIOUS AND NEWLY-FORMED SMALL SWIRLS NOTED IN SATELLITE IMAGERY AND RECON DATA. THE INITIAL INTENSITY OF 40 KT IS BASED ON AN EARLIER NOAA DROPSONDE REPORT OF 40 KT IN THE NORTHEAST QUADRANT. THE INITIAL MOTION ESTIMATE IS 295/10 KT BASED ON A 24-HOUR TREND. OTHER THAN THE UNCERTAINTY IN THE EXACT LOCATION OF OPHELIA... THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. A LARGE SPREAD REMAINS IN THE NHC MODEL GUIDANCE WITH THE GFS AND GFS ENSEMBLE MODELS ALONG THE SOUTHERN EDGE OF THE GUIDANCE ENVELOP INDICATING MORE WESTWARD MOTION...WHEREAS THE GFDL AND HWRF MODELS ARE ON THE FAR RIGHT SIDE INDICATING A MORE NORTHERLY TRACK. THE REMAINDER OF THE GUIDANCE IS SPREAD OUT EVENLY BETWEEN THESE TWO EXTREMES. THE OPHELIA CIRCULATION IS EXPECTED TO MOVE NORTHWESTWARD AND EVENTUALLY NORTHWARD AROUND THE SOUTHWESTERN PERIPHERY OF A LARGE SUBTROPICAL RIDGE THAT IS FORECAST TO WEAKEN AND SHIFT SLOWLY EASTWARD THROUGHOUT THE FORECAST PERIOD. THE OFFICIAL FORECAST TRACK IS LEFT OF THE PREVIOUS ADVISORY...AND LIES DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE CLOSE TO THE CONSENSUS MODEL..TVCN. ALTHOUGH THE CONVECTIVE PATTERN IS SOMEWHAT RAGGED IN OVERALL APPEARANCE...NEW CONVECTION HAS BEEN DEVELOPING IN THE INNER CORE REGION NEAR THE ALLEGED LOW-LEVEL CENTER...WHICH MIGHT PRODUCE SOME SHORT TERM STRENGTHENING. IN THE LONGER TERM...HOWEVER...VERTICAL SHEAR IS EXPECTED TO GRADUALLY INCREASE FROM THE SOUTHWEST THROUGH THE NEXT 72 HOURS...WHICH SHOULD INDUCE GRADUAL WEAKENING. SINCE OPHELIA HAS BEEN ABLE TO MAINTAIN A FAIRLY LARGE CIRCULATION...ANY WEAKENING SHOULD BE LESS THAN WHAT WOULD USUALLY OCCUR FOR A MORE TYPICAL TROPICAL CYCLONE. AFTER THAT TIME...SOME OF THE GLOBAL MODELS...LIKE THE ECMWF...ARE STILL FORECASTING AN UPPER-LEVEL TROUGH NORTH OF THE LESSER ANTILLES TO FRACTURE...WHICH ALLOWS A SMALL ANTICYCLONE TO DEVELOP ABOVE OPHELIA. THIS SCENARIO IS EXPECTED TO RESULT IN SOME RESTRENGTHENING OF THE CYCLONE AT 96 AND 120 HOURS WHILE THE OPHELIA IS STILL OVER SSTS OF 28C. THE INTENSITY FORECAST LEANS TOWARD THE INTENSITY CONSENSUS MODEL ICON. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 17.9N 57.4W 40 KT 45 MPH 12H 25/0600Z 18.7N 58.8W 40 KT 45 MPH 24H 25/1800Z 19.6N 60.4W 40 KT 45 MPH 36H 26/0600Z 20.5N 61.6W 35 KT 40 MPH 48H 26/1800Z 21.4N 62.7W 35 KT 40 MPH 72H 27/1800Z 23.0N 64.0W 35 KT 40 MPH 96H 28/1800Z 24.5N 64.5W 40 KT 45 MPH 120H 29/1800Z 27.0N 64.5W 50 KT 60 MPH $$ FORECASTER STEWART |
