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| #222693 (Received by flhurricane at: 4:34 PM 17.Oct.2008) TCDAT5 HURRICANE OMAR DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL152008 500 PM EDT FRI OCT 17 2008 OMAR HAS EXHIBITED A DISTINCT EYE FEATURE...ALBEIT EMBEDDED IN WEAK CONVECTION...IN BOTH CONVENTIONAL AND TRMM MICROWAVE IMAGERY. A SATELLITE INTENSITY ESTIMATE OF T4.0/65 KT SUPPORTS MAKING OMAR A HURRICANE AGAIN. THE 1601Z TRMM OVERPASS THAT DEPICTED A WELL-DEFINED CLOSED LOW- AND MID-LEVEL EYE FEATURE SUGGESTS THAT OMAR WAS LIKELY A HURRICANE AT 12Z AS WELL. THE INITIAL MOTION VECTOR IS 030/25. NOW THAT CONVECTION HAS STARTED TO WEAKEN...MAKING THE VERTICAL CIRCULATION MORE SHALLOW...THE FORWARD SPEED IS EXPECTED TO GRADUALLY DECREASE AS THE CORRESPONDING STEERING FLOW ALSO WEAKENS. AN UPPER-LEVEL SHORTWAVE TROUGH IS NOW PASSING DIRECTLY OVER OMAR...AND THIS FEATURE IS FORECAST TO CONTINUE LIFTING OUT QUICKLY TO THE NORTHEAST. BEHIND THE TROUGH...THE STEERING FLOW IS EXPECTED TO WEAKEN...WHICH SHOULD RESULT IN A CONTINUED GRADUAL DECREASE IN FORWARD SPEED FOR THE NEXT 48 HOURS. BY 72 HOURS...OMAR IS FORECAST TO TURN MORE EASTWARD WITHIN DEEP-LAYER WESTERLY FLOW IN ADVANCE OF THE NEXT EXTRATROPICAL STORM SYSTEM THAT IS EXPECTED TO EMERGE OFF OF THE U.S. EAST COAST ON SUNDAY-MONDAY. THIS LATTER SYSTEM IS FORECAST BY MOST OF THE GLOBAL MODELS TO MOVE EASTWARD AND GRADUALLY ABSORB OMAR IN 96 TO 120 HOURS. THE OFFICIAL TRACK FORECAST IS SIMILAR IN FORWARD SPEED TO THE NHC MODEL CONSENSUS...BUT LIES TO THE LEFT OF THE MODEL CONSENSUS DUE TO A PERCEIVED SHARP SOUTHWARD TRACK BIAS AND TURN BY THE NOGAPS MODEL...ESPECIALLY AFTER 72 HOURS. THE 65-KT INTENSITY RECENTLY ACHIEVED BY OMAR IS EXPECTED TO BE SHORT-LIVED DUE TO THE LACK OF DEEP CONVECTION AND THE FACT THAT THE CYCLONE WILL BE MOVING OVER SUB-26C SSTS IN 12 HOURS...IF NOT SOONER. ALTHOUGH THE DEEP CONVECTION HAS BEEN DECAPITATED BY AN UPPER-LEVEL SHORTWAVE TROUGH THAT IS CURRENTLY PASSING OVER THE CYCLONE...ONCE THAT FEATURE MOVES AWAY FROM OMAR...A RE-FIRING OF SIGNIFICANT CONVECTION IS EXPECTED TO OCCUR LATER TONIGHT. FOR THAT REASON...THE INTENSITY IS NOT BEING FORECAST TO DECREASE TOO QUICKLY SIMPLY BASED ON THE CURRENT POOR SATELLITE SIGNATURE. IN THE LONGER TERM...HOWEVER...STEADY WEAKENING THROUGHOUT THE FORECAST PERIOD APPEARS LIKELY DUE TO DECREASING SSTS BENEATH THE CYCLONE AND INCREASING VERTICAL WIND SHEAR...ESPECIALLY BY 36 TO 48 HOURS. THE OFFICIAL INTENSITY FORECAST IS IN BEST AGREEMENT WITH THE LGEM STATISTICAL MODEL AND THE HWRF DYNAMICAL MODEL. FORECAST POSITIONS AND MAX WINDS INITIAL 17/2100Z 31.2N 53.6W 65 KT 12HR VT 18/0600Z 32.9N 52.2W 60 KT 24HR VT 18/1800Z 34.9N 49.9W 55 KT 36HR VT 19/0600Z 36.5N 47.3W 50 KT 48HR VT 19/1800Z 38.0N 44.5W 45 KT...BECOMING EXTRATROPICAL 72HR VT 20/1800Z 39.5N 39.0W 40 KT...EXTRATROPICAL 96HR VT 21/1800Z 39.5N 34.0W 35 KT...EXTRATROPICAL 120HR VT 22/1800Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ FORECASTER STEWART |
