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| #386835 (Received by flhurricane at: 4:38 AM 01.Nov.2010) TCDAT1 TROPICAL STORM TOMAS DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL212010 500 AM AST MON NOV 01 2010 WESTERLY VERTICAL SHEAR...WHICH APPEARS TO BE PRIMARILY DUE TO THE DIFFERENCES BETWEEN THE LOWER- AND MID-TROPOSPHERIC FLOW... CONTINUES TO IMPACT TOMAS. CONSEQUENTLY THE CYCLONE REMAINS HIGHLY DECOUPLED AS THE LOW-LEVEL CENTER IS DISPLACED MORE THAN 100 N MI WEST OF THE DEEP CONVECTION. SFMR OBSERVATIONS FROM AN AIR FORCE RECONNAISSANCE AIRCRAFT INDICATE THAT THE INTENSITY HAS DECREASED TO NEAR 45 KT. ADDITIONAL WEAKENING IS LIKELY AS 20 TO 25 KT OF SHEAR SHOULD CONTINUE AFFECTING THE TROPICAL CYCLONE FOR ABOUT ANOTHER 24 HOURS. THEREAFTER...THE SHIPS/LGEM GUIDANCE INDICATES THAT THE SHEAR SHOULD RELAX WHICH WOULD ALLOW FOR TOMAS TO REGAIN STRENGTH. THE OFFICIAL INTENSITY FORECAST FOLLOWS THIS SCENARIO AND IS CLOSE TO THE CONSENSUS OF THE NUMERICAL INTENSITY GUIDANCE. THIS IS WELL ABOVE THE LGEM GUIDANCE AND BELOW THE MORE AGGRESSIVE GFDL MODEL FORECAST. IT SHOULD BE NOTED THAT THERE IS CONSIDERABLE UNCERTAINTY AS TO HOW STRONG TOMAS WILL GET IN THE LATTER PART OF THE FORECAST PERIOD. AIRCRAFT AND SATELLITE FIXES INDICATE THAT THE MOTION IS JUST SLIGHTLY SOUTH OF DUE WEST OR 280/12. A WEAKENING LOW- TO MID-LEVEL RIDGE TO THE NORTH OF THE STORM SHOULD PRODUCE A GENERALLY WESTWARD MOTION WITH DECELERATION OVER THE NEXT 48 HOURS OR SO. IN 72 TO 96 HOURS...THE GLOBAL MODELS DEPICT A LARGE AMPLITUDE MID-TROPOSPHERIC TROUGH MOVING EASTWARD ACROSS THE GULF OF MEXICO. THE FLOW AHEAD OF THIS FEATURE SHOULD TURN TOMAS NORTHWARD AND NORTH-NORTHEASTWARD WITH AN INCREASE IN FORWARD SPEED. THE OFFICIAL FORECAST IS SOMEWHAT SOUTH OF THE PREVIOUS ONE IN THE EARLY PART OF THE FORECAST PERIOD MAINLY DUE TO THE SOUTHWARD SHIFT IN RECENT FIXES. AS NOTED EARLIER...THERE IS SOME AGREEMENT AMONGST THE TRACK MODELS ON THE GENERAL TRAJECTORY OF TOMAS DURING THE LATTER PART OF THE FORECAST PERIOD BUT THERE ARE STILL SUBSTANTIAL DIFFERENCES IN THE PREDICTED FORWARD SPEEDS. DUE TO THE UNCERTAINTIES ONE SHOULD NOT FOCUS ON THE EXACT FORECAST TRACK...PARTICULARLY THE TIMING OF THE 4 AND 5 DAY POINTS. FORECAST POSITIONS AND MAX WINDS INITIAL 01/0900Z 13.8N 67.7W 45 KT 12HR VT 01/1800Z 14.1N 69.3W 40 KT 24HR VT 02/0600Z 14.3N 71.3W 35 KT 36HR VT 02/1800Z 14.4N 72.9W 40 KT 48HR VT 03/0600Z 14.6N 73.9W 45 KT 72HR VT 04/0600Z 15.5N 74.5W 55 KT 96HR VT 05/0600Z 17.5N 74.0W 70 KT 120HR VT 06/0600Z 21.5N 71.5W 65 KT $$ FORECASTER PASCH |
