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| #386526 (Received by flhurricane at: 4:50 PM 30.Oct.2010) TCDAT1 HURRICANE TOMAS DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL212010 500 PM AST SAT OCT 30 2010 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING TOMAS THIS AFTERNOON FOUND MAXIMUM 700 MB FLIGHT-LEVEL WINDS OF 67 KT IN THE NORTH QUADRANT...WHICH EQUATES TO ABOUT 60 KT SURFACE WINDS. SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T4.0/65 KT FROM TAFB AND SAB. THE STRUCTURE OF TOMAS HAS IMPROVED CONSIDERABLY IN RADAR IMAGERY FROM MARTINIQUE...AND THE CYCLONE NOW POSSESSES A CLOSED 25 N MI DIAMETER EYE. THE INTENSITY IS BEING HELD AT 65 KT FOR THIS ADVISORY...WHICH COULD BE A LITTLE LOW BASED ON SOME OF THE DAMAGE REPORTS THAT HAVE BEEN RECEIVED FROM HAM RADIO OPERATORS ON ST. LUCIA AND ST. VINCENT. THE INITIAL MOTION ESTIMATE IS 290/09. TOMAS REMAINS ON TRACK... AND THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. THE LOW- TO MID-LEVEL RIDGE TO THE NORTH OF TOMAS IS EXPECTED TO CONTINUE TO BUILD WESTWARD ACROSS THE GREATER ANTILLES FOR THE NEXT 96 HOURS...WHICH SHOULD KEEP TOMAS ON A WEST-NORTHWEST TO WESTWARD TRACK. HOWEVER...A BROAD LONGWAVE TROUGH CURRENTLY ALONG THE U.S. WEST COAST IS EXPECTED TO MOVE EASTWARD AND THEN SOUTHEASTWARD INTO THE SOUTHEASTERN UNITED STATES...AND PINCH OFF A CLOSED LOW OVER THE GULF OF MEXICO AND SOUTHEASTERN MEXICO BY 120 HOURS. THE STRONG SOUTHWESTERLY FLOW ON THE EAST SIDE OF THE AFOREMENTIONED TROUGH AND LOW IS EXPECTED TO RESULT IN A SIGNIFICANT EROSION OF THE WESTERN PORTION OF THE GREATER ANTILLES RIDGE AND CAUSE THE STEERING CURRENTS ACROSS THE WESTERN AND CENTRAL CARIBBEAN SEA TO WEAKEN...ALLOWING TOMAS TO SLOW DOWN CONSIDERABLY AND BEGIN TO MOVE POLEWARD. MOST OF THE MODEL GUIDANCE IS IN GOOD AGREEMENT ON THIS GENERAL TRACK SCENARIO EXCEPT FOR SPEED DIFFERENCES. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS ADVISORY TRACK...AND REMAINS ALONG THE SOUTHERN EDGE OF THE NHC GUIDANCE ENVELOPE...BUT NOT AS FAR SOUTH AS THE GFS AND ECMWF MODELS. WITH A CLOSED EYE AND A FAVORABLE UPPER-LEVEL ENVIRONMENT...TOMAS IS FORECAST TO STRENGTHEN FOR THE NEXT 24 HOURS OR SO BEFORE WEAK WESTERLY 400-300 MB WINDS UNDERCUT THE IMPRESSIVE OUTFLOW LAYER AND ENTRAINMENT OF DRY MID-LEVEL AIR FROM THE WEST COMBINE TO INTERRUPT THE STRENGTHENING PROCESS. HOWEVER...BY 48-72 HOURS...ENVIRONMENTAL CONDITIONS ARE FORECAST TO IMPROVE...WHICH SHOULD ALLOW TOMAS TO RESUME STEADY INTENSIFICATION. THE GFS-BASED SHIPS AND LGEM MODELS ARE FORECASTING STEADY WEAKENING AFTER 48 HOURS...BUT THAT IS BELIEVED TO BE DUE TO ERRONEOUS MODEL-INDUCED SOUTHWESTERLY VERTICAL SHEAR AFFECTING TOMAS AS A RESULT OF THE OFFICIAL FORECAST TRACK BEING ABOUT 120 N MI NORTH OF THE LARGE SCALE UPPER-LEVEL ANTICYCLONE DEPICTED IN THE GFS MODEL. THE INTENSITY FORECAST REMAINS ABOVE THE SHIPS/LGEM MODELS...AND IS SIMILAR TO THE PREVIOUS FORECAST AND LAST TWO GFDL MODEL RUNS. FORECAST POSITIONS AND MAX WINDS INITIAL 30/2100Z 13.5N 61.4W 65 KT 12HR VT 31/0600Z 14.0N 63.4W 75 KT 24HR VT 31/1800Z 14.5N 65.7W 80 KT 36HR VT 01/0600Z 14.9N 67.9W 80 KT 48HR VT 01/1800Z 15.2N 69.7W 85 KT 72HR VT 02/1800Z 15.7N 72.4W 90 KT 96HR VT 03/1800Z 16.0N 74.0W 95 KT 120HR VT 04/1800Z 16.5N 74.5W 100 KT $$ FORECASTER STEWART |
