000 WTNT41 KNHC 301501 TCDAT1 HURRICANE TOMAS DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL212010 1100 AM AST SAT OCT 30 2010 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING TOMAS THIS MORNING FOUND MAXIMUM 700 MB FLIGHT-LEVEL WINDS OF 68 KT IN THE SOUTHEAST QUADRANT ALONG WITH SEVERAL 64-66 KT RELIABLE SFMR WINDS. IN ADDITION...A DROPSONDE IN THE NORTHEAST EYEWALL INDICATED A SURFACE WIND OF 72 KT. HOWEVER...THE BOUNDARY-LAYER WIND PROFILES SUGGEST A SLIGHTLY LESSER SURFACE WIND SPEED ESTIMATE OF AROUND 66 KT. A COMBINATION OF THIS DATA EASILY SUPPORTS A 65-KT HURRICANE... AND TOMAS HAS BEEN UPGRADED ACCORDINGLY. THE INITIAL MOTION ESTIMATE IS 290/13. THE LATEST RECON FIX POSITIONS HAVE COME IN RIGHT ON THE PREVIOUS ADVISORY TRACK. UPPER-AIR DATA FROM SAN JUAN REVEALED 30-METER 500 MB HEIGHT INCREASES DURING THE PAST 24 HOURS...WHICH CLEARLY INDICATES THAT MID-LEVEL RIDGING TO THE NORTH OF TOMAS HAS STARTED AS THE DEEP-LAYER TROUGH THAT HAS CAPTURED HURRICANE SHARY LIFTS RAPIDLY TO THE NORTHEAST AWAY FROM THE CARIBBEAN REGION. LOW- TO MID-LEVEL RIDGING IS FORECAST BY ALL OF THE GLOBAL MODELS TO CONTINUE BUILDING WESTWARD ACROSS THE LESSER AND GREATER ANTILLES FOR THE NEXT 72-96 HOURS. THIS SHOULD GRADUALLY FORCE TOMAS ON A MORE WESTERLY TRACK...ESPECIALLY AFTER 48 HOURS. HOWEVER...BY DAY 5...A BROAD MID-TROPOSPHERIC TROUGH CURRENTLY LOCATED ALONG THE U.S. WEST COAST IS FORECAST TO MOVE EASTWARD INTO THE CENTRAL U.S. BY DAYS 2-3 AND THEN DIG MORE SOUTHEASTWARD AFTER THAT...AND INTO THE GULF OF MEXICO AND SOUTHEASTERN MEXICO BY DAY 5. THIS IS EXPECTED TO RESULT IN A SIGNIFICANT EROSION OF THE WESTERN PORTION OF THE RIDGE AND A WEAKENING OF THE STEERING CURRENT ACROSS THE WESTERN AND CENTRAL CARIBBEAN SEA. THIS WEAK FLOW REGIME SHOULD ALLOW TOMAS TO SLOW DOWN AND GRADUALLY MOVE NORTHWARD. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE AND EXTENSION OF THE PREVIOUS ADVISORY TRACK... AND REMAINS ALONG THE SOUTHERN EDGE OF THE NHC GUIDANCE ENVELOPE. TOMAS HAS DEVELOPED A 30-40 NMI DIAMETER EYE NOTED IN RECENT RADAR IMAGES FROM MARTINIQUE. THE UPPER-LEVEL OUTFLOW PATTERN IS WELL ESTABLISHED AND CONTINUES TO IMPROVE. A COMBINATION OF THE AFOREMENTIONED FEATURES ALONG WITH DEEP WARM WATER AHEAD OF THE CYCLONE SHOULD RESULT IN CONTINUED STRENGTHENING FOR THE NEXT 24 HOURS OR SO. AFTER THAT...HOWEVER...WESTERLY 300 MB WINDS ARE EXPECTED TO UNDERCUT THE IMPRESSIVE OUTFLOW LAYER AND INDUCE SOME SHEAR ON TOMAS...WHICH MAY HALT THE INTENSIFICATION PROCESS. USUALLY WITH WESTERLY SHEAR COMES DRY AIR MID-LEVEL AIR...AND THIS INHIBITING FACTOR WAS CLEARLY INDICATED IN UPPER-AIR DATA WEST OF 65W LONGITUDE THIS MORNING. BY 72 HOURS...ENVIRONMENTAL CONDITIONS ARE EXPECTED TO IMPROVE AS TOMAS SLOWS DOWN...AND A INTENSIFICATION IS EXPECTED TO RESUME. THE OFFICIAL INTENSITY FORECAST IS ABOVE THE SHIPS/LGEM MODELS...AND IS SIMILAR TO THE PREVIOUS FORECAST AND LAST TWO GFDL MODEL RUNS...WHICH MAKES A TOMAS A MAJOR HURRICANE SOUTH OF HISPANIOLA. FORECAST POSITIONS AND MAX WINDS INITIAL 30/1500Z 13.3N 60.7W 65 KT 12HR VT 31/0000Z 13.8N 62.5W 75 KT 24HR VT 31/1200Z 14.4N 64.8W 80 KT 36HR VT 01/0000Z 14.8N 67.2W 80 KT 48HR VT 01/1200Z 15.2N 69.2W 85 KT 72HR VT 02/1200Z 15.6N 72.3W 90 KT 96HR VT 03/1200Z 16.0N 74.0W 100 KT 120HR VT 04/1200Z 16.5N 75.0W 100 KT $$ FORECASTER STEWART