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Tropical Storm NICHOLAS


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TROPICAL STORM NICHOLAS DISCUSSION NUMBER  20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SAT OCT 18 2003
 
IN A BIT OF A SUNRISE SURPRISE...MORNING VISIBLE IMAGERY SHOWS THE
CENTER OF NICHOLAS IS LOCATED SOUTHEAST OF THE PREVIOUS ADVISORY
POSITION...WHICH REQUIRES A RE-LOCATION.  THE CENTER HAS BECOME
EXPOSED AS MODERATE/STRONG SOUTHWESTERLY VERTICAL SHEAR HAS
DISRUPTED THE CDO PATTERN SEEN EARLIER.  SATELLITE INTENSITY
ESTIMATES ARE 55 KT FROM SAB...AND 65 KT FROM TAFB AND AFWA.  THE
INITIAL INTENSITY REMAINS 55 KT...ALTHOUGH WITH THE CURRENT
APPEARANCE THIS MAY BE GENEROUS.

WITH THE RE-LOCATION...THE INITIAL MOTION IS A HIGHLY UNCERTAIN
015/3.  SURFACE OBSERVATIONS SUGGEST SOME STRENGTHENING OF THE
LOW-LEVEL RIDGE NORTH OF NICHOLAS...WHILE WATER VAPOR IMAGERY SHOWS
A LARGE MID/UPPER-LEVEL RIDGE DEVELOPING OVER THE CENTRAL ATLANTIC
AS A LARGE TROUGH DEVELOPS OVER THE WESTERN ATLANTIC AND EASTERN
UNITED STATES.  ADDITIONALLY...A BROAD UPPER-LEVEL RIDGE IS ALONG
44W SOUTH OF 22N.  THIS COMPLEX PATTERN WILL LIKELY CONTINUE THE
SLOW MOTION OF NICHOLAS...AND THE BUILDING RIDGE TO THE NORTH
SUGGESTS THE CYCLONE SHOULD RESUME A MORE WESTWARD TRACK IN THE
NEXT 24-36 HR.  TRACK GUIDANCE REMAINS SPREAD.  THE GFS TAKES
NICHOLAS WESTWARD...WHILE THE NOGAPS MOVES IT DUE NORTHWARD.  THE
UKMET AND THE GFDL CALL FOR A GENERAL NORTHWESTWARD MOTION THROUGH
72 HR...AND THE FORECAST TRACK THROUGH THAT TIME IS IN BEST
AGREEMENT WITH THEM.  AFTER 120 HR...THE FORECAST TRACK CALLS FOR A
CONTINUED NORTHWEST MOTION.  HOWEVER...A LARGE NON-TROPICAL CYCLONE
DEVELOPING OFF THE U.S. EAST COAST COULD CAUSE NICHOLAS TO TURN
MORE NORTHWARD THAN CURRENTLY FORECAST.

WHILE NICHOLAS SHOWS ANTICYCLONIC OUTFLOW EVEN TO THE SOUTHWEST...
THE FLOW ASSOCIATED WITH THE UPPER-LEVEL RIDGE IS UNDERCUTTING THE
OUTFLOW AND SHEARING THE STORM.  THE LARGE-SCALE MODELS CONTINUE TO
FORECAST A SHORT-TERM DECREASE IN THE SHEAR.  SO FAR...THESE
FORECASTS HAVE NOT VERIFIED...AND THERE ARE NO OBVIOUS SIGNS THAT
THEY ARE GOING TO VERIFY NOW.  THE INTENSITY FORECAST IS BASED ON
THE PREMISE THAT CONTINUED MODERATE/STRONG WESTERLY SHEAR WILL
CONTINUE THROUGH THE FORECAST PERIOD AND CAUSE GRADUAL WEAKENING.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/1500Z 16.9N  47.7W    55 KT
 12HR VT     19/0000Z 17.4N  47.8W    55 KT
 24HR VT     19/1200Z 18.1N  48.2W    50 KT
 36HR VT     20/0000Z 18.8N  48.8W    50 KT
 48HR VT     20/1200Z 19.5N  49.6W    45 KT
 72HR VT     21/1200Z 20.5N  51.0W    40 KT
 96HR VT     22/1200Z 21.5N  52.5W    35 KT
120HR VT     23/1200Z 22.5N  54.0W    30 KT
 
 
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