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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