Tropical Storm NICHOLAS

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TROPICAL STORM NICHOLAS DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT OCT 18 2003

AS HAS HAPPENED THE PAST TWO AFTERNOONS...A NEW BURST OF CONVECTION
HAS DEVELOPED OVER THE LOW-LEVEL CENTER OF NICHOLAS.  HOWEVER...THE
STORM LOOKS A LITTLE LESS ORGANIZED THAN IT DID 24 HR AGO...AND
SATELLITE INTENSITY ESTIMATES HAVE DECREASED...ESPECIALLY FROM
TAFB.  THIS DECREASE IS SUPPORTED BY EXPERIMENTAL INTENSITY
ESTIMATES FROM ADVANCED MICROWAVE SOUNDING UNIT DATA FROM THE NOAA
POLAR ORBITING SATELLITES.  THE MAXIMUM WINDS ARE REDUCED TO 50 KT.
 
THE INITIAL MOTION IS NOW 360/3.  SURFACE OBSERVATIONS SHOW A
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
45W SOUTH OF 21N.  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 IS A LITTLE LESS SPREAD THAN
EARLIER...AS THE NOGAPS...GFDL...AND UKMET NOW GENERALLY AGREE ON A
NORTHWESTWARD TO NORTHWARD MOTION.  EVEN THE WESTWARD-POINTING GFS
NOW SHOWS A MORE NORTHWARD TURN BY THE END OF THE FORECAST PERIOD
IN RESPONSE TO A DEVELOPING NON-TROPICAL CYCLONE OFF THE U.S. EAST
COAST.  THE OFFICIAL FORECAST NOW CALLS FOR A TURN TOWARD THE
NORTHWEST DURING THE FIRST 24 HR....THEN A TURN TOWARD THE
NORTH-NORTHWEST AFTER 72 HR.

NICHOLAS NOW SHOWS NO OUTFLOW OVER THE WESTERN SEMICIRCLE AS
SOUTHWESTERLY TO WESTERLY SHEAR CONTINUES TO IMPACT IT.  THE
LARGE-SCALE MODELS CONTINUE TO FORECAST A SHORT-TERM DECREASE IN
SHEAR THAT HAS JUST NOT OCCURRED.  THE INTENSITY FORECAST WILL
CONTINUE TO BE BASED ON THE PREMISE THAT MODERATE/STRONG WESTERLY
SHEAR WILL LAST THROUGH THE FORECAST PERIOD AND CAUSE GRADUAL
WEAKENING.  IT SHOULD BE NOTED THAT THE MODELS FORECAST A SHORTWAVE
TROUGH NOW OVER THE EASTERN CARIBBEAN TO MOVE EAST-NORTHEAST AND
INTERACT WITH NICHOLAS.  HOWEVER...THE DETAILS DIFFER ENOUGH
BETWEEN THE MODELS THAT IT IS NOT CURRENTLY POSSIBLE TO TELL
WHETHER THIS WILL HELP THE STORM OR HURT IT.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/2100Z 17.3N  47.7W    50 KT
 12HR VT     19/0600Z 17.7N  47.9W    50 KT
 24HR VT     19/1800Z 18.4N  48.4W    45 KT
 36HR VT     20/0600Z 19.1N  49.1W    45 KT
 48HR VT     20/1800Z 19.7N  49.7W    40 KT
 72HR VT     21/1800Z 21.0N  51.0W    40 KT
 96HR VT     22/1800Z 22.5N  52.0W    35 KT
120HR VT     23/1800Z 24.5N  53.0W    30 KT
 
 
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