000
WTNT45 KNHC 172032
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