000
WTNT41 KNHC 010841
TCDAT1
TROPICAL STORM TOMAS DISCUSSION NUMBER  13...CORRECTED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL212010
500 AM AST MON NOV 01 2010

CORRECTED MOTION TO 260/12
 
WESTERLY VERTICAL SHEAR...WHICH APPEARS TO BE PRIMARILY DUE TO THE
DIFFERENCES BETWEEN THE LOWER- AND MID-TROPOSPHERIC FLOW...
CONTINUES TO IMPACT TOMAS.  CONSEQUENTLY THE CYCLONE REMAINS HIGHLY
DECOUPLED AS THE LOW-LEVEL CENTER IS DISPLACED MORE THAN 100 N MI
WEST OF THE DEEP CONVECTION.  SFMR OBSERVATIONS FROM AN AIR FORCE
RECONNAISSANCE AIRCRAFT INDICATE THAT THE INTENSITY HAS DECREASED
TO NEAR 45 KT.  ADDITIONAL WEAKENING IS LIKELY AS 20 TO 25 KT OF
SHEAR SHOULD CONTINUE AFFECTING THE TROPICAL CYCLONE FOR ABOUT
ANOTHER 24 HOURS.  THEREAFTER...THE SHIPS/LGEM GUIDANCE INDICATES
THAT THE SHEAR SHOULD RELAX WHICH WOULD ALLOW FOR TOMAS TO REGAIN
STRENGTH.  THE OFFICIAL INTENSITY FORECAST FOLLOWS THIS SCENARIO
AND IS CLOSE TO THE CONSENSUS OF THE NUMERICAL INTENSITY GUIDANCE.
THIS IS WELL ABOVE THE LGEM GUIDANCE AND BELOW THE MORE AGGRESSIVE
GFDL MODEL FORECAST.  IT SHOULD BE NOTED THAT THERE IS CONSIDERABLE
UNCERTAINTY AS TO HOW STRONG TOMAS WILL GET IN THE LATTER PART OF
THE FORECAST PERIOD.
 
AIRCRAFT AND SATELLITE FIXES INDICATE THAT THE MOTION IS JUST
SLIGHTLY SOUTH OF DUE WEST OR 260/12.  A WEAKENING LOW- TO
MID-LEVEL RIDGE TO THE NORTH OF THE STORM SHOULD PRODUCE A
GENERALLY WESTWARD MOTION WITH DECELERATION OVER THE NEXT 48 HOURS
OR SO.  IN 72 TO 96 HOURS...THE GLOBAL MODELS DEPICT A LARGE
AMPLITUDE MID-TROPOSPHERIC TROUGH MOVING EASTWARD ACROSS THE GULF OF
MEXICO.  THE FLOW AHEAD OF THIS FEATURE SHOULD TURN TOMAS NORTHWARD
AND NORTH-NORTHEASTWARD WITH AN INCREASE IN FORWARD SPEED.  THE
OFFICIAL FORECAST IS SOMEWHAT SOUTH OF THE PREVIOUS ONE IN THE
EARLY PART OF THE FORECAST PERIOD MAINLY DUE TO THE SOUTHWARD SHIFT
IN RECENT FIXES.  AS NOTED EARLIER...THERE IS SOME AGREEMENT
AMONGST THE TRACK MODELS ON THE GENERAL TRAJECTORY OF TOMAS DURING
THE LATTER PART OF THE FORECAST PERIOD BUT THERE ARE STILL
SUBSTANTIAL DIFFERENCES IN THE PREDICTED FORWARD SPEEDS.  DUE TO
THE UNCERTAINTIES ONE SHOULD NOT FOCUS ON THE EXACT FORECAST
TRACK...PARTICULARLY THE TIMING OF THE 4 AND 5 DAY POINTS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/0900Z 13.8N  67.7W    45 KT
 12HR VT     01/1800Z 14.1N  69.3W    40 KT
 24HR VT     02/0600Z 14.3N  71.3W    35 KT
 36HR VT     02/1800Z 14.4N  72.9W    40 KT
 48HR VT     03/0600Z 14.6N  73.9W    45 KT
 72HR VT     04/0600Z 15.5N  74.5W    55 KT
 96HR VT     05/0600Z 17.5N  74.0W    70 KT
120HR VT     06/0600Z 21.5N  71.5W    65 KT
 
$$
FORECASTER PASCH