000 WTNT41 KNHC 030840 TCDAT1 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