ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM TROPICAL STORM FIONA DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082010 1100 AM AST WED SEP 01 2010 EARLIER THIS MORNING...THE AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT MEASURED A PEAK 850 MB WIND OF 58 KT...BELIEVABLE SFMR VALUES OF 45-50 KT...AND A MINIMUM PRESSURE OF 998 MB. THIS WAS THE BASIS FOR THE 8 AM INTENSITY OF 50 KT. SINCE THAT TIME... THE SYSTEM HAS BECOME MORE DISORGANIZED WITH THE CENTER ON THE NORTHWESTERN EDGE OF WEAKENING DEEP CONVECTION. ANOTHER AIRCRAFT WILL BE IN THE SYSTEM EARLY THIS AFTERNOON. DESPITE MODERATE SHEAR...ALL OF THE GUIDANCE SHOW FURTHER INTENSIFICATION AND MOST ACTUALLY MAKE FIONA A HURRICANE. BY LATE TOMORROW...THE SHEAR SHOULD INCREASE AS THE MAJORITY OF THE GLOBAL MODELS HAVE FAIRLY STRONG NORTHEASTERLY SHEAR IN A FEW DAYS DUE PRIMARILY TO STRONG UPPER-LEVEL WINDS FROM EARL. THIS PATTERN CAUSES FIONA TO RAPIDLY WEAKEN IN 3 OR 4 DAYS...AND THE NHC FORECAST WILL STAY ON THE LOWER END OF THE GUIDANCE ENVELOPE...FAIRLY CLOSE TO THE SHIPS MODEL. AIRCRAFT FIXES SHOW A MOTION OF ABOUT 305/15 DURING THE PAST SEVERAL HOURS. TRACK MODELS ARE IN GOOD AGREEEMENT ON A NORTHWEST TO NORTH-NORTHWEST MOTION FOR A DAY OR TWO DUE TO FIONA MOVING AROUND A SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC OCEAN. HOWEVER...THE GUIDANCE STARTS TO BECOME RATHER DIVERGENT AFTER THAT TIME...WHICH APPEARS TO BE RELATED TO THE FUTURE INTENSITY OF FIONA. IF THE STORM WEAKENS QUICKLY...THE LOW-LEVEL CIRCULATION WILL LIKELY GET CAUGHT UP IN SOUTHWESTERLY FLOW AHEAD OF EARL. HOWEVER...IF FIONA STAYS A MORE COHERENT VORTEX...THERE REMAINS THE POTENTIAL FOR IT TO GET TRAPPED BY A MID-LEVEL SUBTROPICAL RIDGE. GIVEN THE STRONG SHEAR FORECAST AT THE END...THE NHC FORECAST LEANS TOWARD THE FASTER TRACK SCENARIO AT THE END OF THE FORECAST PERIOD AND IS CLOSE TO THE PREVIOUS FORECAST. HOWEVER...I DO NOT HAVE A LOT OF CONFIDENCE IN THE LONG-TERM TRACK OR INTENSITY FORECASTS...AS THE MODELS HAVE BEEN STURGGLING WITH CONSISTENCY WITH THIS STORM. FORECAST POSITIONS AND MAX WINDS INITIAL 01/1500Z 18.8N 61.7W 50 KT 12HR VT 02/0000Z 20.3N 63.3W 55 KT 24HR VT 02/1200Z 22.6N 65.3W 55 KT 36HR VT 03/0000Z 24.9N 66.6W 55 KT 48HR VT 03/1200Z 26.9N 67.1W 45 KT 72HR VT 04/1200Z 29.0N 67.0W 40 KT 96HR VT 05/1200Z 31.0N 67.0W 30 KT 120HR VT 06/1200Z...DISSIPATED $$ FORECASTER BLAKE NNNN
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