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| #34848 (Received by flhurricane at: 4:37 AM 23.Jul.2005) TCDAT1 TROPICAL STORM FRANKLIN DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SAT JUL 23 2005 FRANKLIN...THE STORM...NOT THE FORECASTER...HAS BECOME A LITTLE BETTER ORGANIZED OVERNIGHT. REPORTS FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT A FEW HOURS AGO INDICATE THAT THE WIND FIELD HAS BECOME MORE SYMMETRIC WHILE THE PRESSURE CONTINUED A SLOW BUT STEADY FALL...TO 1001 MB AT 05Z. THE PEAK 850 MB FLIGHT LEVEL WINDS WERE 57 KT IN THE NORTHEAST QUADRANT...WHICH SUPPORTS A SOLID 45 KT AS THE SURFACE ESTIMATE. THE RECONNAISSANCE FIXES INDICATE THAT FRANKLIN HAS TURNED TO THE NORTH-NORTHEAST...WITH AN INITIAL MOTION ESTIMATED TO BE 030/7. THE SYNOPTIC ENVIRONMENT OF THE CYCLONE IS COMPLICATED...RESULTING IN CONSIDERABLE UNCERTAINTY IN BOTH THE TRACK AND INTENSITY FORECASTS. A MID-LATITUDE SHORT-WAVE TROUGH THAT EXTENDS THROUGH THE CAROLINAS IS ABOUT TO MOVE EASTWARD INTO THE ATLANTIC. IN THE SHORT TERM...THIS IS EXPECTED TO FORCE FRANKLIN TO TURN TO THE NORTHEAST. HOWEVER...THIS TROUGH WILL ALSO BRING CONSIDERABLE VERTICAL SHEAR WITH IT...AND BY 36-48 HOURS...THE CYCLONE WILL FIND ITSELF UNDER AN UNFAVORABLE UPPER-LEVEL NORTHERLY OR NORTHWESTERLY FLOW. IN FACT...WATER VAPOR IMAGERY ALREADY IS SHOWING A RESTRICTION OF THE UPPER-LEVEL OUTFLOW TO THE NORTH OF FRANKLIN. THE FUTURE TRACK OF FRANKLIN IS VERY MUCH TIED TO HOW IT RESPONDS TO THIS IMPENDING SHEAR...AND THE MODEL GUIDANCE IS HIGHLY DIVERGENT. THE GFS DECOUPLES THE CYCLONE'S LOW AND MID-LEVEL CIRCULATIONS AND RACES A WEAK SYSTEM EAST-NORTHEASTWARD IN THE LOW-LEVEL FLOW. THE NOGAPS AND UKMET MODELS MAINTAIN A STRONGER...MORE VERTICALLY CONNECTED SYSTEM THAT ALSO MOVES TO THE EAST-NORTHEAST BUT MUCH MORE SLOWLY. THE GFDL HAS A RATHER SURPRISING SOLUTION IN THAT IT IS BOTH RELATIVELY FAST WITH THE EASTWARD MOTION AND YET ALSO FORECASTS FRANKLIN TO ATTAIN AND THEN MAINTAIN HURRICANE STRENGTH FOR ALMOST 72 HOURS. SO WHAT TO DO WITH THIS RANGE OF POSSIBILITIES? SMALL SYSTEMS ARE FREQUENTLY NOT THAT RESISTENT TO SHEAR. THE OFFICIAL FORECAST IS THEREFORE CONSIDERABLY FASTER THAN THE NOGAPS OR UKMET GUIDANCE. HOWEVER...THE GFS IS ALREADY TOO FAST...SO PERHAPS NONE OF THE INDIVIDUAL DYNAMICAL MODELS HAVE A GOOD HANDLE ON THIS PARTICULAR FORECAST. THE OFFICIAL FORECAST IS A PRIMARILY A BLEND OF CONTINUITY FROM THE PREVIOUS FORECAST...THE SHALLOW BAM...THE GUNA CONSENSUS...AND THE FSU SUPERENSEMBLE...AND IS ONLY COINCIDENTALLY CLOSE TO THE GFDL. THE FORECAST TRACK HAS BEEN SHIFTED SOMEWHAT SOUTHWARD...AND DOES SHOW A CLOSE APPROACH TO BERMUDA IN 72 HOURS. IT IS WORTH NOTING HOWEVER...THAT SOME OF THE LARGEST TRACK ERRORS OCCUR IN HIGH-SHEAR SCENARIOS SUCH AS THIS ONE. THE CENTER OF CIRCULATION IS WELL EMBEDDED IN A SMALL CIRCULAR AREA OF DEEP CONVECTION...AND EARLIER RECONNAISSANCE DATA SUGGESTED THAT THE CYCLONE WAS GETTING READY TO STRENGTHEN. CONSEQUENTLY...THE SHORT-TERM PROSPECTS FOR INTENSIFICATION ARE GOOD. HOWEVER...THE OPPORTUNITY FOR DEVELOPMENT IN THE LONG RUN APPEARS LIMITED...WITH AN INCREASE IN SHEAR AND A DECREASE IN SSTS SEEMINGLY IN THE CYCLONE'S FUTURE. IT IS QUITE POSSIBLE THAT LITTLE OR NOTHING WILL BE LEFT OF FRANKLIN...THE STORM...NOT THE FORECASTER...IN 2-3 DAYS. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 23/0900Z 29.1N 75.9W 45 KT 12HR VT 23/1800Z 30.0N 74.8W 55 KT 24HR VT 24/0600Z 30.8N 73.0W 60 KT 36HR VT 24/1800Z 31.4N 71.0W 60 KT 48HR VT 25/0600Z 31.8N 69.0W 55 KT 72HR VT 26/0600Z 32.5N 65.0W 50 KT 96HR VT 27/0600Z 35.0N 60.5W 45 KT 120HR VT 28/0600Z 39.0N 56.0W 40 KT |
