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Tropical Storm FRANKLIN


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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
 
 
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