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Tropical Storm NICHOLAS (Text)

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TROPICAL STORM NICHOLAS DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT THU OCT 16 2003
 
NICHOLAS HAS CHANGED LITTLE IN ORGANIZATION THIS MORNING AS THE
SYSTEM REMAINS AFFECTED BY SOUTHWESTERLY VERTICAL SHEAR.  THE
LOW-LEVEL CENTER IS NEAR THE WESTERN EDGE OF A LARGE AREA OF
PERSISTENT CONVECTION WITH TOPS COLDER THAN -80C.  THE OUTFLOW
ANTICYCLONE SEEN YESTERDAY IS LESS IMPRESSIVE LOOKING TODAY...
ALTHOUGH THE OUTFLOW IS STILL GOOD OVER THE NORTHEASTERN
SEMICIRCLE.  SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND
AFWA...AND 45 KT FROM SAB.  THE INITIAL INTENSITY REMAINS 50 KT.

THE INITIAL MOTION IS 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 ALONG 21N51W-12N61W CAUSING SOUTHWESTERLY
UPPER-LEVEL FLOW NEAR NICHOLAS.  TRACK GUIDANCE RESPONDS TO THIS
COMPLEX BALANCE OF STEERING FLOWS WITH A SPREAD.  THE NHC98UK AND
BAMS FORECAST CONTINUED NORTHWESTWARD MOTION...WHILE THE NOGAPS...
GFDN...AND LBAR CALL FOR A NORTHEASTWARD TURN.  THE OTHER
MODELS ARE IN BETWEEN.  GIVEN THE SHEARED STATE OF THE CYCLONE...
AND THAT THE NOGAPS HAS SHOWN A SIGNIFICANT NORTHWARD BIAS ON THIS
STORM...THE OFFICIAL FORECAST WILL CONTINUE TO CALL FOR A GENERAL
NORTHWESTWARD TO NORTH-NORTHWESTWARD MOTION.  NICHOLAS WILL LIKELY
TURN A LITTLE TO THE RIGHT AS THE CURRENT MID/UPPER-LEVEL RIDGE
NORTH OF THE CYCLONE PUSHES EASTWARD...THEN TURN A BIT BACK TO THE
LEFT IN ABOUT 36 HR AS THE NEXT SHORTWAVE RIDGE PASSES TO THE
NORTH.  ANOTHER BEND TO THE RIGHT IS POSSIBLE AFTER 72 HR AS
NICHOLAS MAKES CONTACT WITH THE WESTERLIES NORTH OF 20N.  THE
FORECAST TRACK IS AN UPDATE OF THE PREVIOUS PACKAGE AND IS IN BEST
AGREEMENT WITH THE UKMET.

LARGE-SCALE MODELS HAVE A VARIETY OF SOLUTIONS FOR THE UPPER-LEVEL
FLOW NEAR NICHOLAS...RANGING FROM THE FAVORABLE ANTICYCLONE OF THE
UKMET TO THE LESS FAVORABLE LOOK OF THE GFS AND CANADIAN.  THE 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.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/1500Z 13.8N  46.2W    50 KT
 12HR VT     17/0000Z 14.8N  47.0W    55 KT
 24HR VT     17/1200Z 15.9N  47.8W    60 KT
 36HR VT     18/0000Z 16.7N  48.3W    65 KT
 48HR VT     18/1200Z 17.5N  49.1W    65 KT
 72HR VT     19/1200Z 18.5N  50.5W    65 KT
 96HR VT     20/1200Z 20.0N  51.5W    65 KT
120HR VT     21/1200Z 22.0N  52.0W    60 KT
 
 
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