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TROPICAL STORM OLGA DISCUSSION NUMBER 32
NATIONAL WEATHER SERVICE MIAMI FL
10 AM EST SUN DEC 02 2001
OLGA REFUSES TO GO AWAY. CONVENTIONAL AND MICROWAVE SATELLITE
IMAGERY INDICATE THAT OLGA HAS BECOME BETTER ORGANIZED...DESPITE THE
MORE SUBTROPICAL APPEARANCE...AND HAS ALSO STRENGTHENED. OLGA HAS
MOVED UNDERNEATH AND MERGED WITH AN UPPER-LEVEL LOW...HENCE THE MORE
SUBTROPICAL APPEARANCE IN SATELLITE IMAGERY. THE INITIAL INTENSITY
WAS INCREASED TO 40 KT BASED ON A BLEND OF DVORAK SATELLITE
INTENSITY ESTIMATES OF 35 KT...T2.5...FROM ALL THREE AGENCIES AND
DATA T-NUMBERS OF 3.0...OR 45 KT...A 02/0947 QUIKSCAT OVERPASS
INDICATING SEVERAL UNCONTAMINATED 40 KT WIND VECTORS...AND SHIP PGHT
REPORTING A PRESSURE OF 1001.1 MB NEAR THE CENTER AT 02/12Z. OUTFLOW
HAS ALSO IMPROVED IN ALL QUADRANTS AND IS NOW MORE SYMMETRICAL.
THE INITIAL MOTION IS 345/07. A LARGE MID-LEVEL ANTICYCLONE IS
SITUATED ABOUT 600 NM EAST OF OLGA AND IS ACTING TO LIFT THE SYSTEM
NORTH-NORTHWESTWARD. WATER VAPOR IMAGERY CURRENTLY INDICATES A
STRONG SHORTWAVE TROUGH OVER INDIANA MOVING EASTWARD AT 40 KT IN
STRONG ZONAL FLOW. EXTRAPOLATION OF THIS FEATURE WOULD PLACE THE
TROUGH DUE NORTH OF OLGA IN ABOUT 24 HOURS...A LITTLE FASTER THAN
THE 06Z AVN MODEL RUN IS INDICATING...AND CLOSE TO THE UKMET AND
NOGAPS POSITIONS. THE RESULT IS THAT THE WEAKNESS IN THE 500 MB
RIDGE TO THE NORTH SHOULD DISAPPEAR IN ABOUT 36 TO 48 HOURS...
CAUSING OLGA TO UNFORTUNATELY SLOW DOWN AND TURN BACK TO THE WEST...
POSSIBLY EVEN LOOPING AGAIN. HOWEVER...ALL OF THE GLOBAL MODELS
AGREE ON THE SURFACE TO 700 MB RIDGE AXIS REMAINING INTACT THROUGH
THE PERIOD AND THAT SHOULD PREVENT OLGA FROM RECURVING NORTHEASTWARD
AND GETTING CAUGHT UP IN THE STRONG POLAR WESTERLIES. THE OFFICIAL
FORECAST TRACK IS SLIGHTLY EAST OF THE PREVIOUS TRACK THROUGH 48
HOURS...AND THEN TURNS OLGA BACK TO THE WEST SIMILAR TO THE PREVIOUS
FORECAST AFTER THAT. THIS IS CONSISTENT WITH THE AVN...GFDL...AND
GFDN MODEL SUITE...EXCEPT THAT MORE WEIGHT WAS PLACED ON THE AVN.
THE INTENSITY FORECAST IS AS COMPLICATED AS THE TRACK FORECAST. I AM
UNCERTAIN WHETHER OR NOT OLGA WILL GO BACK TO A SUBTROPICAL CYCLONE
THAT COULD RESIST VERTICAL SHEAR...OR REMAIN A WARM-CORE TROPICAL
CYCLONE WHICH WOULD MAKE VERTICAL SHEAR A SIGNIFCANT FACTOR IN THE
INTENSITY FORECAST. THE SHIPS INTENSITY MODEL RAPIDLY WEAKENS AND
DISSIPATES THE CYCLONE IN 60 TO 72 HOURS...WHICH IT HAS BEEN DOING
FOR THE PAST 36 HOURS...YET OLGA HAS CONTINUED TO STRENGTHEN. THE
AVN AND GFDN KEEP THE CYCLONE BETWEEN 50 AND 40 KT...RESPECTIVELY...
THROUGH 48 HOURS WITH ONLY SLOW WEAKENING BELOW TROPICAL STORM
STRENGTH BY 72 HOURS. THAT SCENARIO WAS FOLLOWED CLOSELY. HOWEVER...
IF THE AVN MODEL IS CORRECT IN BUILDING A 200 MB ANTICYCLONE OVER
THE SYSTEM IN 72 HOURS AND BEYOND...THE DECREASING VERTICAL SHEAR
AND MORE FAVORABLE OUTFLOW PATTERN COULD KEEP OLGA ONGOING FOR
SEVERAL MORE DAYS. AS SUCH...THE ONSET OF DISSIPATION WAS PUSHED
BACK TO THE 72 HOUR TIME PERIOD.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 02/1500Z 25.9N 69.3W 40 KTS
12HR VT 03/0000Z 26.9N 69.6W 45 KTS
24HR VT 03/1200Z 27.8N 69.6W 45 KTS
36HR VT 04/0000Z 28.4N 69.5W 40 KTS
48HR VT 04/1200Z 28.7N 69.5W 35 KTS
72HR VT 05/1200Z 28.5N 71.5W 30 KTS...DISSIPATING
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