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Tropical Storm NICHOLAS

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TROPICAL STORM NICHOLAS DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT THU OCT 16 2003
 
VERTICAL SHEAR SEEMS TO HAVE DECREASED A LITTLE NEAR NICHOLAS THIS
AFTERNOON.  CIRRUS CLOUD MOTIONS SHOW A MORE SOUTHERLY THAN
SOUTHWESTERLY FLOW WEST OF THE CYCLONE...AND THE UPPER-LEVEL
ANTICYLONE OVER THE STORM LOOKS MORE HEALTHY THAN 6 HR AGO. 
NICHOLAS HAS RESPONDED TO THIS BY CHANGING FROM A SHEAR PATTERN TO
A CURVED CONVECTIVE BAND.  SATELLITE INTENSITY ESTIMATES ARE ALL 55
KT...SO THAT IS THE INITIAL INTENSITY.

THE INITIAL MOTION REMAINS 310/7.  SATELLITE IMAGERY AND SURFACE
OBSERVATIONS INDICATE NICHOLAS IS SOUTH OF A WEAK LOW/MID-LEVEL
RIDGE.  WATER VAPOR IMAGERY SHOWS A SERIES OF RIDGES AND TROUGHS IN
THE WESTERLIES ACROSS THE ATLANTIC NORTH OF 20N...AND AN UPPER-LEVEL
TROUGH/SHEAR AXIS FROM 21N52W TO A VORTEX NEAR 11N62W.  TRACK
GUIDANCE CONTINUES TO RESPOND TO THIS COMPLEX BALANCE OF STEERING
FLOWS WITH A SPREAD...WITH MANY OF THE SAME OUTLIERS AS 6 HR AGO.
THE BIGGEST CHANGES IS THAT THE 12Z GFS AND UKMET FORECAST A MORE
WESTWARD MOTION THAN THEIR PREVIOUS RUNS.  UNTIL THIS TREND IS
CONFIRMED BY SUBSEQUENT RUNS...THE OFFICIAL FORECAST WILL NOT SHOW
A MAJOR SHIFT.  THE FORECAST TRACK IS AN UPDATE OF THE PREVIOUS
PACKAGE.
 
LARGE-SCALE MODELS CONTINUE TO HAVE A VARIETY OF SOLUTIONS FOR THE
UPPER-LEVEL FLOW NEAR NICHOLAS.  THE LESS-FAVORABLE LOOKING GFS
AND CANADIAN APPEAR TO HAVE THE BEST HANDLE ON THE FLOW...SO THE
INTENSITY FORECAST LEANS HEAVILY ON THEIR SHEAR FORECASTS.  THESE
MODELS FORECAST A GRADUAL DECREASE IN THE SHEAR FOR 24-36 HR...AND
STRONG SHEAR N OF 20N LATER IN THE FORECAST PERIOD.  BASED ON
THIS...THE INTENSITY FORECAST WILL CALL FOR 24-36 HR OF SLOW
STRENGTHENING TO MINIMAL HURRICANE STRENGTH.  IT WILL ALSO CALL FOR
THE START OF A WEAKENING TREND AFTER 96 HR.  THIS INTENSITY FORECAST
IS STRONGER THAN THAT OF SHIPS...BUT WEAKER THAN THAT OF THE GFDL.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/2100Z 14.4N  47.0W    55 KT
 12HR VT     17/0600Z 15.3N  47.7W    60 KT
 24HR VT     17/1800Z 16.4N  48.3W    65 KT
 36HR VT     18/0600Z 17.3N  49.1W    65 KT
 48HR VT     18/1800Z 18.0N  49.9W    65 KT
 72HR VT     19/1800Z 19.0N  51.0W    65 KT
 96HR VT     20/1800Z 20.5N  52.0W    65 KT
120HR VT     21/1800Z 22.0N  52.5W    60 KT
 
 
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