548
WTNT45 KNHC 152044
TCDAT5
HURRICANE OMAR DISCUSSION NUMBER 10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL152008
500 PM EDT WED OCT 15 2008
TWO RECENT PASSES THROUGH OMAR'S EYE INDICATE THE CENTRAL PRESSURE
DECREASED BY AT LEAST 4 MB...DOWN TO 973 MB. THE AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT ALSO MEASURED A PEAK 700 MB FLIGHT-LEVEL
WIND OF 89 KT IN THE SOUTHEAST QUADRANT...WHICH EQUATES TO ABOUT AN
80-KT SURFACE WIND...DESPITE THE HIGHEST SFMR SURFACE MEASURED
HAVING ONLY BEEN 74 KT. HOWEVER...THE RECON AIRCRAFT AND THE
CONVECTION HAVE BEEN PLAYING A GAME OF CAT-AND-MOUSE...AND I DO NOT
BELIEVE THAT THE AIRCRAFT HAS BEEN SAMPLING THE STRONGEST WINDS IN
THE STRONGEST CONVECTION. THE ADVISORY INTENSITY HAS BEEN INCREASED
TO 80 KT...WHICH COULD BE A LITTLE LOW GIVEN THAT THE PRESSURE-WIND
RELATIONSHIP FOR 973 MB CORRESPONDS TO ABOUT 85 KT.
THE INITIAL MOTION ESTIMATE IS 050/013. AFTER AN EARLIER JOG TO THE
EAST-NORTHEAST...IT APPEARS THAT OMAR HAS RESUMED ITS BASE COURSE
BACK TOWARD THE NORTHEAST. THERE REMAINS NO SIGNIFICANT CHANGE TO
THE PREVIOUS TRACK FORECAST OR PHILOSOPHY AS ALL OF THE TRACK
MODELS REMAIN TIGHTLY CLUSTERED ABOUT A NORTHEASTWARD MOTION
THROUGH THE NORTHERN LEEWARD ISLANDS AND THE VIRGIN ISLANDS IN
12-18 HOURS HOURS. AFTER THAT...OMAR IS FORECAST TO ACCELERATE AS
IT GETS DRAWN RAPIDLY NORTHEASTWARD IN SOUTHWESTERLY STEERING FLOW
ON THE EAST SIDE OF A LARGE MID-TROPOSPHERIC TROUGH THAT IS
FORECAST TO MOVE OFF THE U.S. EAST COAST AND INTO THE WESTERN AND
CENTRAL ATLANTIC BY DAY 3. DURING DAYS 4-5...OMAR IS EXPECTED TO
ACCELERATE THE EAST-NORTHEAST OR EASTWARD AT FORWARD SPEEDS IN
EXCESS OF 35 KT AND BECOME EXTRATROPICAL OVER THE MUCH COOLER
WATERS OF THE NORTH ATLANTIC. THE OFFICIAL FORECAST TRACK IS
SLIGHTLY TO THE RIGHT OF PREVIOUS TRACK...AND REMAINS SLOWER THAN
THE NHC MODEL CONSENSUS...WHICH HAS HAD A NOTICEABLE FAST FORWARD
SPEED BIAS.
STRONG CONVECTIVE BURSTS HAVE CONTINUED TO DEVELOP IN THE EYEWALL
AND RADAR DATA FROM SAN JUAN HAS INDICATED OCCASIONAL DISTINCT
MESOVORTICES ROTATING AROUND THE INNER PORTION OF THE EYEWALL. THIS
FAVORABLE SMALL-SCALE INTENSIFICATION SHOULD PERSISTS FOR ANOTHER
12 HOURS OR SO...WHICH MEANS THAT OMAR HAS A GOOD CHANCE OF
REACHING AT LEAST CATEGORY 2 INTENSITY BEFORE IT MOVES THROUGH THE
NORTHERN LEEWARD ISLANDS LATER TONIGHT AND THURSDAY MORNING. THE
GFDL MODEL WAS MUCH MORE BULLISH WITH OMAR ON THE 12Z MODEL RUN AND
BRINGS THE HURRICANE UP TO 109 KT BY 18-24 HOURS. THAT MUCH
INTENSIFICATION IS LIKELY OVERDONE GIVEN SATELLITE INDICATIONS OF A
RAPIDLY SHRINKING CDO FEATURE...PLUS THE INTRUSION OF DRY MID-LEVEL
INTO THE NORTHWEST QUADRANT OF THE CYCLONE. HOWEVER...SINCE OMAR IS
EXPECTED TO REMAIN IN A RELATIVELY LOW SHEAR ENVIRONMENT AND OVER
29C SSTS...ADDITIONAL STRENGTHENING TO 90 KT SEEMS VERY PLAUSIBLE
...AND WOULD MOST LIKELY OCCUR LATER TONIGHT DURING THE USUAL
NOCTURNAL CONVECTIVE MAXIMUM PERIOD. ALSO...INTERESTS IN THE
LEEWARD ISLANDS ARE REMINDED THAT STRONGER WINDS...POSSIBLY ONE
CATEGORY HIGHER...CAN BE EXPECTED OVER HIGHER TERRAIN...ESPECIALLY
ABOVE 500 FT ELEVATION.
FORECAST POSITIONS AND MAX WINDS
INITIAL 15/2100Z 15.9N 66.1W 80 KT
12HR VT 16/0600Z 17.6N 64.8W 85 KT...NRN LEEWARD ISLANDS
24HR VT 16/1800Z 20.4N 62.9W 90 KT
36HR VT 17/0600Z 23.2N 60.9W 90 KT
48HR VT 17/1800Z 26.1N 59.2W 85 KT
72HR VT 18/1800Z 31.7N 54.8W 75 KT
96HR VT 19/1800Z 39.0N 44.5W 60 KT...BECOMING EXTRATROPICAL
120HR VT 20/1800Z 48.0N 27.0W 50 KT...EXTRATROPICAL
FORECASTER STEWART
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