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| #461040 (Received by flhurricane at: 4:59 AM 22.Sep.2011) TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 500 AM AST THU SEP 22 2011 ALTHOUGH OPHELIA IS NOT WELL ORGANIZED ON SATELLITE IMAGES WITH ALL OF THE CONVECTION LOCATED NORTHEAST OF THE CENTER...NOAA BUOY 41041 REPORTED PEAK ONE-MINUTE SUSTAINED WINDS OF 54 KT WITH A GUST TO 68 KT DURING THE PAST COUPLE OF HOURS. THUS THE INITIAL INTENSITY IS INCREASED TO 55 KT FOR THIS ADVISORY...AND THIS MIGHT BE A LITTLE CONSERVATIVE GIVEN THE REMOTE CHANCES OF MEASURING THE INTENSITY OF A SYSTEM WITH JUST ONE OBSERVING STATION. THE INTENSIFICATION OF OPHELIA IS EXPECTED TO BE SHORT-LIVED AS SOUTHWESTERLY VERTICAL WIND SHEAR SHOULD INCREASE OVER THE NEXT DAY OR SO. GLOBAL MODELS ARE IN GOOD AGREEMENT ON A MID-OCEANIC UPPER-LEVEL TROUGH REMAINING ENHANCED FOR THE NEXT SEVERAL DAYS...WHICH SHOULD CAUSE SOME WEAKENING OF THE TROPICAL CYCLONE. AT THE END OF THE FORECAST PERIOD...THE MID-OCEANIC TROUGH COULD FRACTURE...RESULTING IN A LOWER SHEAR ENVIRONMENT MORE CONDUCIVE FOR STRENGTHENING. THE NHC INTENSITY FORECAST SHOWS WEAKENING EARLY ON...AND IS CLOSEST TO THE FSU SUPERENSEMBLE...ON THE LOW SIDE OF THE GUIDANCE ENVELOPE. IT WOULD NOT BE SURPRISING IF OPHELIA ENDED UP WEAKENING FASTER THAN SHOWN BELOW GIVEN THE SOMEWHAT HOSTILE UPPER-LEVEL WINDS EXPECTED. MICROWAVE AND ASCAT DATA INDICATED THAT THE CENTER IS A LITTLE FARTHER SOUTH THAN ANTICIPATED...WHICH REQUIRED A SMALL REPOSITIONING OF THE CENTER. THIS CHANGE RESULTS IN AN ESTIMATED MOTION OF 275/12. MOST OF THE RELIABLE GUIDANCE SHOW OPHELIA TURNING TO THE WEST-NORTHWEST BY FRIDAY MORNING AS THE MID-LEVEL RIDGE WEAKENS SOMEWHAT. A TURN TO THE NORTHWEST IS ANTICIPATED OVER THE WEEKEND DUE TO THE TROPICAL CYCLONE REACHING THE SOUTHWESTWARD EDGE OF THE SUBTROPICAL RIDGE...WITH A MORE POLEWARD TRACK ANTICIPATED FOR EARLY NEXT WEEK. THERE IS FAIR AGREEMENT IN THE GLOBAL MODEL GUIDANCE ON THIS SOLUTION...THOUGH THE SPEED DIFFERENCES ARE NOTABLE BY DAY 5. THE NHC TRACK FORECAST IS SHIFTED TO THE RIGHT AFTER 24 HOURS...BUT REMAINS TO THE WEST OF THE DYNAMICAL MODEL CONSENSUS...AND THE TOP-PERFORMING ECMWF/GFS MODELS. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 13.4N 47.0W 55 KT 65 MPH 12H 22/1800Z 13.8N 49.0W 55 KT 65 MPH 24H 23/0600Z 14.5N 51.6W 50 KT 60 MPH 36H 23/1800Z 15.4N 53.8W 50 KT 60 MPH 48H 24/0600Z 16.7N 55.8W 45 KT 50 MPH 72H 25/0600Z 19.3N 59.6W 45 KT 50 MPH 96H 26/0600Z 21.5N 63.0W 45 KT 50 MPH 120H 27/0600Z 24.5N 65.5W 50 KT 60 MPH $$ FORECASTER BLAKE |
