000 WTNT41 KNHC 212032 TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 500 PM AST WED SEP 21 2011 OPHELIA HAS CHANGED LITTLE IN ORGANIZATION OVER THE PAST SEVERAL HOURS...WITH A PORTION OF THE INNER CORE LOW-LEVEL CIRCULATION STILL EXPOSED OVER THE SOUTHWEST SEMICIRCLE. RECENT IMAGES SHOW THAT THE CENTER IS LOCATED JUST UNDER THE SOUTHWEST EDGE OF THE CONVECTIVE CANOPY. MODERATE SOUTH-SOUTHWESTERLY SHEAR...ASSOCIATED WITH AN UPPER-LEVEL TROUGH TO THE NORTHWEST OF THE STORM...IS FORECAST TO CONTINUE TO AFFECT OPHELIA THROUGH THE FORECAST PERIOD. THEREFORE NO STRENGTHENING IS FORECAST...WITH SOME WEAKENING LIKELY IN A FEW DAYS. SINCE THE CURRENT LGEM GUIDANCE IS A LITTLE HIGHER THAN THE PREVIOUS ONE...THE NHC WIND FORECAST NOW SHOWS LESS WEAKENING IN 3-5 DAYS. TWO MODEL EXTREMES HIGHLIGHT THE UNCERTAINTIES IN PREDICTING INTENSITY CHANGE. THE EXPERIMENTAL COAMPS-TC MODEL...WHICH HAS BEEN A GOOD PERFORMER SO FAR THIS YEAR...SHOWS DISSIPATION BY 72 HOURS WHILE THE GFDL MODEL PREDICTS OPHELIA TO BECOME A MAJOR HURRICANE BY THE END OF THE FORECAST PERIOD. INITIAL MOTION REMAINS AROUND 280/14 AS THE STORM REMAINS SOUTH OF A SUBTROPICAL HIGH PRESSURE SYSTEM. OPHELIA IS LIKELY TO MOVE ON A WESTWARD TO WEST-NORTHWESTWARD TRACK OVER THE NEXT SEVERAL DAYS...ALONG THE SOUTHERN PERIPHERY OF THE HIGH. LATE IN THE FORECAST PERIOD...AS THE CYCLONE NEARS THE SOUTHWESTERN PERIPHERY OF THE RIDGE...THE DYNAMICAL GUIDANCE IS LEANING MORE TO THE RIGHT OF PREVIOUS RUNS. THE LATEST OFFICIAL FORECAST IS A LITTLE TO THE NORTH...OR RIGHT...OF THE PREVIOUS ONE BUT NOT AS FAR TO THE RIGHT AS MOST OF THE TRACK MODELS BY DAY 5. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 13.6N 44.7W 50 KT 60 MPH 12H 22/0600Z 13.8N 46.8W 50 KT 60 MPH 24H 22/1800Z 14.1N 49.4W 50 KT 60 MPH 36H 23/0600Z 14.6N 51.8W 50 KT 60 MPH 48H 23/1800Z 15.5N 54.0W 50 KT 60 MPH 72H 24/1800Z 17.5N 58.5W 45 KT 50 MPH 96H 25/1800Z 20.0N 62.5W 45 KT 50 MPH 120H 26/1800Z 22.5N 65.5W 45 KT 50 MPH $$ FORECASTER PASCH