304 
 WTNT41 KNHC 302046
 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