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Tropical Storm OPHELIA (Text)

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TROPICAL STORM OPHELIA DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
500 PM AST FRI SEP 23 2011
 
DEEP CONVECTION HAS REDEVELOPED NEAR AND OVER THE LOW-LEVEL CENTER
DURING THE PAST 6 HOURS...AND REPORTS FROM AN AIR FORCE RESERVE
RECONNAISSANCE AIRCRAFT INDICATE THE INTENSITY HAS INCREASED TO 50
KT BASED ON FLIGHT-LEVEL WINDS OF 60 KT AND BELIEVABLE SFMR SURFACE
WINDS OF 50-51 KT.
 
THE INITIAL MOTION IS 285/13...AFTER ONCE AGAIN HAVING TO SMOOTH
THROUGH ALL OF THE WIGGLES AND WOBBLES IN THE TRACK. THE
DEVELOPMENT OF THE DEEP CONVECTION NEAR THE CENTER LIKELY PULLED
THE BARELY-CLOSED LOW-LEVEL CIRCULATION CENTER NORTHWESTWARD...
WHICH IS BELIEVED TO BE A TEMPORARY MOTION.  OTHERWISE...THERE HAS
BEEN NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK. MOST OF
THE MODEL GUIDANCE SHIFTED TO THE RIGHT DUE TO THE MORE NORTHWARD
INITIAL POSITION...BUT THE SUBTROPICAL RIDGE TO THE NORTH OF
OPHELIA IS FORECAST BY ALL OF THE GLOBAL MODELS TO REMAIN QUITE
STRONG...WHICH SHOULD KEEP THE CYCLONE MOVING IN A GENERAL
WEST-NORTHWESTWARD MOTION FOR THE NEXT 48 HOURS OR SO. BY 72 HOURS
AND BEYOND...THE WESTERN PORTION OF THE RIDGE IS FORECAST TO ERODE
AS A MID-/UPPER-LEVEL TROUGH MOVES EASTWARD ACROSS FLORIDA AND THE
BAHAMAS. THIS SHOULD CAUSE OPHELIA TO SLOW DOWN AND TURN
NORTHWESTWARD BY DAYS 3-4...AND THEN ALLOW FOR A GRADUAL NORTHWARD
TURN BY DAY 5. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE
PREVIOUS ADVISORY TRACK...AND LIES NEAR THE SOUTHERN OR LEFT SIDE
OF THE NHC GUIDANCE ENVELOPE.

ALTHOUGH THE GFS-BASED SHIPS MODEL IS ASSESSING NEAR 20 KT OF
SOUTHWESTERLY SHEAR ACROSS THE CYCLONE...THE UW-CIMSS MID-LEVEL
SHEAR ANALYSES INDICATE THE SHEAR IS 15 KT OR LESS. THIS HAS LIKELY
ALLOWED THE RECENT RESURGENCE IN INNER CORE CONVECTION. HOWEVER...
THIS BRIEF RESPITE IS EXPECTED TO BE SHORT-LIVED AS ALL OF THE
GLOBAL MODELS ARE FORECASTING THE VERTICAL SHEAR TO INCREASE TO
MORE THAN 25 KT IN 12-18 HOURS. THERE WILL CONTINUE TO BE
FLUCTUATIONS IN THE MAGNITUDE OF THE VERTICAL SHEAR FOR THE NEXT 96
HOURS...WHICH WILL RESULT IN THE WAXING AND WANING OF THE CENTRAL
DEEP CONVECTION...BUT THE GENERAL TREND SHOULD BE FOR GRADUAL
WEAKENING TO OCCUR. HOWEVER...BY DAY 5...SOME SLIGHT STRENGTHENING
IS POSSIBLE AS THE SHEAR DECREASES AND OPHELIA MOVES UNDERNEATH OR
NEAR A SMALL UPPER-LEVEL ANTICYCLONE.

FORECAST POSITIONS AND MAX WINDS
 
INIT  23/2100Z 15.5N  53.8W   50 KT  60 MPH
 12H  24/0600Z 16.3N  55.7W   50 KT  60 MPH
 24H  24/1800Z 17.5N  58.0W   45 KT  50 MPH
 36H  25/0600Z 18.6N  60.0W   45 KT  50 MPH
 48H  25/1800Z 19.7N  61.8W   40 KT  45 MPH
 72H  26/1800Z 21.8N  64.9W   40 KT  45 MPH
 96H  27/1800Z 24.0N  66.6W   40 KT  45 MPH
120H  28/1800Z 26.5N  67.5W   45 KT  50 MPH
 
$$
FORECASTER STEWART
 
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