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Tropical Storm NICHOLAS


ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM NICHOLAS DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT FRI OCT 17 2003

AFTER ALMOST LOOKING LIKE A HURRICANE THIS MORNING...NICHOLAS HAS
WEAKENED A LITTLE DUE TO SOUTHWESTERLY VERTICAL SHEAR.  THE
LOW-LEVEL CENTER BECAME EXPOSED FOR A TIME BEFORE BEING COVERED BY
THE LATEST BURST OF CONVECTION.  WHILE SATELLITE INTENSITY
ESTIMATES REMAIN 65 KT...THIS IS BASED MAINLY ON CONSTRAINTS FROM
THE EARLIER ESTIMATES.  THE INITIAL INTENSITY IS REDUCED TO 55 KT. 
IT SHOULD BE NOTED THAT THE CIRRUS OUTFLOW HAS INCREASED ON THE
SOUTHWEST SIDE OF THE CYCLONE...WHICH IS A BIT DECEIVING AS
SOUTHWESTERLY FLOW IS UNDERCUTTING THE OUTFLOW AND CAUSING SHEAR.
 
THE INITIAL MOTION IS 325/7.  THERE IS LITTLE CHANGE IN EITHER THE
SYNOPTIC PATTERN OF THE FORECAST REASONING FROM THE PREVIOUS
PACKAGE.  NICHOLAS IS CAUGHT IN A COMPLEX PATTERN OF SURROUNDING
WEATHER SYSTEMS THAT COMBINE TO PRODUCE WEAK STEERING CURRENTS.
THE TRACK GUIDANCE SHOWS GREATER SPREAD THAN 6 HR AGO.  AMONGST THE
DYNAMICAL GUIDANCE...THE UKMET AND GFS FORECAST A MOTION TOWARD THE
NORTHWEST OR WEST-NORTHWEST...THE GFDL FORECASTS A TURN TO THE
NORTH...THE NOGAPS CALLS FOR A NORTHEASTWARD MOTION FOLLOWED BY A
NORTHWESTWARD TURN...AND THE GFDN CALLS FOR NORTHWARD TO
NORTHEASTWARD MOTION.  THE KEY FACTOR IN THE SPREAD SEEMS TO BE THE
STRENGTH OF THE STORM...AS THE STRONGER THE STORM IS IN THE MODEL
THE FARTHER EAST IT GOES.  SINCE THE GFS AND UKMET APPEAR TOO WEAK
WITH NICHOLAS...AND THE OTHER DYNAMICAL GUIDANCE APPEARS TOO
STRONG...THE FORECAST TRACK WILL SPLIT THE DIFFERENCE.  THE NEW
FORECAST IS AN UPDATE OF THE PREVIOUS PACKAGE.

AN UPPER-LEVEL RIDGE SOUTHEAST OF NICHOLAS HAS A WELL-DEFINED WIND
MAXIMUM ALONG ITS NORTHERN PERIPHERY.  THIS WIND BAND IS
UNDERCUTTING THE CIRRUS OUTFLOW OF NICHOLAS.  THE FUTURE INTENSITY
DEPENDS ON HOW CLOSE THE STORM STAYS TO THE WIND MAXIMUM.
DYNAMICAL MODELS FORECAST THE RIDGE TO MOVE WESTWARD...WHICH COULD
FORCE THE WIND MAXIMUM NORTH OF THE CYCLONE AND CREATE A MORE
FAVORABLE ENVIRONMENT DURING THE NEXT 48 HR...ESPECIALLY IF
NICHOLAS MOVES SLOWER THAN FORECAST.  CONVERSELY...IF THE STORM
MOVES FASTER THAN FORECAST...IT WOULD REMAIN IN STRONGER SHEAR.
GIVEN THE UNCERTAINTY IN HOW MUCH SHEAR NICHOLAS WILL FACE...AND
THAT IT WILL BE DIFFICULT FOR NICHOLAS TO STRENGTHEN MORE IF THE
SHEAR DOES NOT DECREASE...THE INTENSITY FORECAST IS CHANGED TO THAT
OF A STEADY-STATE 55 KT FOR 72 HR.  AFTER THAT...NICHOLAS WILL
LIKELY ENTER STRONGER SHEAR NORTH OF 20N AND WEAKEN. 
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/2100Z 16.4N  48.5W    55 KT
 12HR VT     18/0600Z 17.1N  48.9W    55 KT
 24HR VT     18/1800Z 17.9N  49.4W    55 KT
 36HR VT     19/0600Z 18.6N  50.0W    55 KT
 48HR VT     19/1800Z 19.2N  50.5W    55 KT
 72HR VT     20/1800Z 20.5N  51.5W    55 KT
 96HR VT     21/1800Z 21.5N  52.5W    50 KT
120HR VT     22/1800Z 23.0N  54.0W    45 KT
 
 
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Page last modified: Monday, 07-Feb-2005 16:50:00 UTC