Tropical Storm Omar: Discussion #15

TROPICAL STORM OMAR DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL152008
1100 AM EDT TUE OCT 14 2008

SATELLITE AND RADAR DATA INDICATE THE DEPRESSION HAS CONTINUED TO
BECOME BETTER ORGANIZED AND CLOUD TOPS HAVE COOLED SIGNIFICANTLY
WITH SOME TOPS TO -86C NEAR THE CENTER. OUTFLOW HAS ALSO IMPROVED
IN ALL QUADRANTS AND IS LESS RESTRICTED TO THE NORTHWEST NOW. THE
INITIAL ADVISORY OF 35 KT IS BASED ON A CONSENSUS T2.5/35 KT
SATELLITE ESTIMATE FROM TAFB AND SAB FOR THE PAST 12 HOURS...PLUS
SEVERAL BELIEVABLE 30-34 KT QUIKSCAT WIND VECTORS NOTED IN THE
NORTHWEST QUADRANT AROUND 1036Z THIS MORNING. THUS...TROPICAL
DEPRESSION FIFTEEN HAS BEEN UPGRADED TO TROPICAL STORM OMAR.

THE INITIAL MOTION ESTIMATE IS 115/02. OMAR HAS BEEN DRIFTING SOUTH
TO SOUTHEASTWARD THE PAST 12 HOURS...AND CURRENTLY SHOWS NO SIGN OF
CHANGING THAT MOTION. HOWEVER...ALL OF THE AVAILABLE MODEL GUIDANCE
INDICATES THAT A BROAD DEEP MID-LATITUDE TROUGH OVER THE CENTRAL
AND WESTERN ATLANTIC WILL CONTINUE TO DROP SOUTHWARD AND GRADUALLY
PICK UP OMAR AND NUDGE IT TO THE EAST DURING THE NEXT 12 HOURS...
AND THEN ACCELERATE IT TO THE NORTHEAST AFTER THAT. THE LATEST
TREND IN WATER VAPOR IMAGERY SUPPORTS THIS SCENARIO AS A PIECE OF
SHORTWAVE ENERGY ALONG 70W LONGITUDE CAN BE SEEN DIGGING DUE SOUTH.
NHC MODEL GUIDANCE IS TIGHTLY CLUSTERED CROSS-WISE...BUT THERE ARE
SIGNIFICANT DIFFERENCES IN THE FORWARD SPEED AND JUST HOW SOON OMAR
GETS PICKED UP BY THE AFOREMENTIONED TROUGH. THE OFFICIAL FORECAST
TRACK HAS BEEN SHIFTED TO THE EAST OR RIGHT OF THE PREVIOUS TRACK
...MAINLY DUE TO THE MORE EASTWARD INITIAL POSITION...BUT NOT AS FAR
EAST OR AS FAST AS THE MODEL CONSENSUS.

RECENT DEVELOPMENT OF A CDO-LIKE AREA OF CENTRAL DEEP CONVECTION
SUGGESTS THAT OMAR MAY BE STARTING A PERIOD OF RAPID STRENGTHENING.
IN ADDITION...A LARGE MASS OF CONVECTION IN THE EASTERN SEMICIRCLE
THAT HAS BEEN DISRUPTING INFLOW INTO THE CIRCULATION CENTER HAS
WEAKENED CONSIDERABLY...WHICH SHOULD ALLOW FOR MORE CONVECTIVE
FORCING TO OCCUR NEAR THE LOW-LEVEL CENTER. THE IMPROVING OUTFLOW
PATTERN AND A FORECAST OF DECREASING VERTICAL WIND SHEAR OF LESS
THAN 10 KT FOR THE NEXT 24 HOURS FURTHER SUPPORTS A FORECAST OF
STEADY INTENSIFICATION OF AT LEAST ONE T-NUMBER PER DAY FOR THE
NEXT 24 HOURS. AFTER THAT...SOUTHWESTERLY VERTICAL WIND SHEAR AHEAD
OF THE LARGE MID-LATITUDE TROUGH IS EXPECTED TO INCREASE TO GREATER
THAN 20 KT...SO THE INTENSIFICATION TREND SHOULD SLOW DOWN BY DAY 2
AND BEYOND. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE
PREVIOUS ADVISORY AND IS A BLEND OF THE SHIPS...GFDL...AND HWRF
MODELS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 14/1500Z 14.0N 69.0W 35 KT
12HR VT 15/0000Z 14.7N 68.3W 45 KT
24HR VT 15/1200Z 15.8N 67.3W 55 KT
36HR VT 16/0000Z 17.3N 65.6W 60 KT
48HR VT 16/1200Z 19.1N 63.6W 65 KT
72HR VT 17/1200Z 23.8N 60.0W 65 KT
96HR VT 18/1200Z 28.0N 58.0W 65 KT
120HR VT 19/1200Z 33.0N 55.0W 65 KT


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