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| #372612 (Received by flhurricane at: 4:56 AM 31.Aug.2010) TCDAT3 TROPICAL STORM FIONA DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082010 500 AM AST TUE AUG 31 2010 FIONA HAS CHANGED LITTLE IN STRUCTURE DURING THE LAST SEVERAL HOURS. DEEP CONVECTION REMAINS CONFINED TO A FEW CURVED BANDS MAINLY OVER THE WESTERN SEMICIRCLE...ALTHOUGH AN AREA OF THUNDERSTORMS HAS RECENTLY FORMED NEAR THE ESTIMATED CENTER POSITION. THE INITIAL INTENSITY IS HELD AT 35 KT...IN AGREEMENT WITH AN 0056 UTC ASCAT PASS AND A 1007 MB PRESSURE REPORT FROM BUOY 41040. ONLY A LITTLE STRENGTHENING IS FORECAST IN THE SHORT TERM DUE TO MARGINALLY FAVORABLE UPPER-LEVEL WINDS...SOME DRY AIR AROUND THE CYCLONE...AND CURRENT LACK OF ORGANIZATION. THE SHIPS MODEL SHOWS NORTHEASTERLY SHEAR INCREASING SIGNIFICANTLY IN 24-36 HOURS...AND IF CORRECT...THAT SHOULD LIMIT ADDITIONAL STRENGTHENING. THIS INTENSITY FORECAST IS UNCHANGED FROM EARLIER AND REMAINS NEAR THE LOW END OF THE MODEL GUIDANCE. THE AFOREMENTIONED ASCAT PASS AND A TRMM OVERPASS AT 0303 UTC SUGGESTED THAT THE LOW-LEVEL CENTER...ALBEIT NOT VERY EASY TO LOCATE...WAS SITUATED A LITTLE TO THE NORTH OF THE PREVIOUS ESTIMATES. THEREFORE...THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 285/20. A NARROW MID-LEVEL RIDGE LOCATED ALONG 25 N OVER THE CENTRAL AND EASTERN ATLANTIC IS EXPECTED TO KEEP FIONA ON A RATHER FAST WEST-NORTHWESTWARD COURSE FOR THE NEXT DAY OR SO. THEREAFTER...THE CYCLONE IS EXPECTED TO APPROACH A WEAKNESS IN THE RIDGE...WHICH WILL BE ENHANCED BY HURRICANE EARL...AND THAT SHOULD CAUSE FIONA TO GRADUALLY SLOW DOWN AND TURN TO THE NORTHWEST. THE ECMWF...WHICH HAS BEEN THE LEFT-MOST MODEL FOR THE PAST COUPLE OF CYCLES...IS NOW ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE. IN GENERAL...THE MODEL GUIDANCE HAS SHIFTED SLIGHTLY TO THE RIGHT AND IS A LITTLE FASTER AT THE END OF THE PERIOD...AND THE NHC FORECAST HAS BEEN ADJUSTED IN THAT DIRECTION. FORECAST POSITIONS AND MAX WINDS INITIAL 31/0900Z 15.8N 53.0W 35 KT 12HR VT 31/1800Z 16.5N 55.7W 35 KT 24HR VT 01/0600Z 17.8N 59.1W 40 KT 36HR VT 01/1800Z 19.6N 61.9W 45 KT 48HR VT 02/0600Z 21.8N 64.2W 45 KT 72HR VT 03/0600Z 26.5N 67.5W 45 KT 96HR VT 04/0600Z 29.0N 68.5W 45 KT 120HR VT 05/0600Z 30.5N 69.0W 45 KT $$ FORECASTER CANGIALOSI/BLAKE |
