Tropical Depression TOMAS

ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION TOMAS DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL212010
500 AM EDT WED NOV 03 2010
 
AN AIR FORCE HURRICANE HUNTER AIRCRAFT INVESTIGATING TOMAS A COUPLE
OF HOURS AGO FOUND AN ILL-DEFINED AND ELONGATED CIRCULATION WITH NO
TROPICAL STORM FORCE WINDS AT EITHER THE 925 MB FLIGHT LEVEL OR THE
SURFACE.  BASED ON THIS INFORMATION...TOMAS IS BEING DOWNGRADED TO
A TROPICAL DEPRESSION AT THIS TIME.   THE PERIPHERAL CLOUD PATTERN
CONTINUES TO SHOW ORGANIZATION WITH FRAGMENTED OUTER BANDS...BUT
THERE IS LITTLE CONVECTIVE ORGANIZATION NEAR THE ESTIMATED CENTER. 
THE WEAKENING OVER THE PAST 24 HOURS IS DIFFICULT TO EXPLAIN. 
PRECIPITABLE WATER ANALYSES FROM THE UW/CIMSS DO NOT SUGGEST MUCH
OF AN INTRUSION OF DRY AIR INTO THE CIRCULATION.  THE CIRRUS
MOTIONS FROM SATELLITE IMAGES SHOW A FAIRLY WELL-DEFINED OUTFLOW
PATTERN...ESPECIALLY OVER THE NORTHERN SEMICIRCLE.  THIS WOULD
NORMALLY BE CONSISTENT WITH LIGHT VERTICAL SHEAR.  AMSU
AREA-AVERAGED WIND SHEAR DERIVED BY CSU/CIRA...HOWEVER...INDICATE A
RECENT INCREASE IN MID- TO UPPER-LEVEL SHEAR OVER TOMAS.  THIS IS
EXPECTED TO BE TEMPORARY AS GLOBAL MODELS PREDICT DECREASING SHEAR
OVER THE NEXT COUPLE OF DAYS.  THE INTENSITY FORECAST CONTINUES TO
CALL FOR TOMAS TO RESTRENGTHEN INTO A HURRICANE BEFORE REACHING
LAND.  GIVEN THE ERRATIC BEHAVIOR OF THIS TROPICAL CYCLONE THUS
FAR...THIS IS A LOW-CONFIDENCE INTENSITY FORECAST.  THE NOAA G-IV
JET IS CURRENTLY CONDUCTING A SYNOPTIC SURVEILLANCE MISSION AROUND
TOMAS WHICH SHOULD GIVE A BETTER ASSESSMENT OF THE DYNAMIC AND
THERMODYNAMIC ENVIRONMENT.

THE HURRICANE HUNTERS FOUND A BROAD AREA OF LIGHT WINDS SURROUNDING
THE LOCATION OF THE MINIMUM PRESSURE...SO THERE IS SIGNIFICANT
UNCERTAINTY IN THE CENTER POSITION AND INITIAL MOTION.  OUR BEST
GUESS AT THE LATTER IS 285/4.  THE TRACK FORECAST IS BASICALLY
UNCHANGED FROM THE PREVIOUS ADVISORY.  TOMAS IS EXPECTED TO TURN
NORTHWARD AND NORTHEASTWARD OVER THE NEXT FEW DAYS IN RESPONSE TO
THE STEERING FLOW AHEAD OF AN APPROACHING MID-TROPOSPHERIC TROUGH. 
BY THE END OF THE FORECAST PERIOD...GLOBAL MODELS SHOW THIS TROUGH
LIFTING OUT AND LEAVING TOMAS BEHIND OVER THE SUBTROPICS FOR A FEW
DAYS.  ACCORDINGLY...THE OFFICIAL TRACK FORECAST SHOWS A TURN TO
THE RIGHT WITH DECREASING FORWARD SPEED BY DAY 5.
 
REGARDLESS OF THE EXACT TRACK AND INTENSITY OF TOMAS...THE TROPICAL
CYCLONE WILL POSE A SIGNIFICANT THREAT OF HEAVY RAINFALL...
FLOODING...AND POTENTIAL MUD SLIDES OVER HAITI AND THE
DOMINICAN REPUBLIC LATER IN THE WEEK.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      03/0900Z 13.5N  75.5W    30 KT
 12HR VT     03/1800Z 13.8N  76.1W    35 KT
 24HR VT     04/0600Z 14.4N  76.5W    40 KT
 36HR VT     04/1800Z 15.3N  76.3W    50 KT
 48HR VT     05/0600Z 16.8N  75.3W    65 KT
 72HR VT     06/0600Z 20.0N  73.0W    65 KT
 96HR VT     07/0600Z 21.5N  71.5W    60 KT
120HR VT     08/0600Z 22.0N  69.5W    50 KT
 
$$
FORECASTER PASCH/ROBERTS
 
NNNN