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HURRICANE OLGA DISCUSSION NUMBER  15
NATIONAL WEATHER SERVICE MIAMI FL
4 AM EST WED NOV 28 2001
 
DVORAK-BASED INTENSITY ESTIMATES FROM TAFB AND SAB ARE T4.5...
CORRESPONDING TO 77 KT.  THE LATEST OBJECTIVE DVORAK ESTIMATES ARE A
LITTLE LOWER AT T4.3...SO THE INITIAL INTENSITY IS SET TO 75 KT FOR
THIS ADVISORY.  SATELLITE IMAGERY SHOWS THAT THE OUTFLOW PATTERN HAS
DETERIORATED SOMEWHAT OVER THE PAST 24 HOURS.  OLGA IS CURRENTLY IN
A LOW-SHEAR UPPER ENVIRONMENT WITHIN A BROAD CYCLONIC CIRCULATION.
HOWEVER...THIS BROAD UPPER PATTERN IS FORECAST TO EVOLVE INTO A
SHARP AND ELONGATED TROUGH THAT SHOULD EXPOSE THE HURRICANE TO
INCREASING SHEAR WITHIN 36 HOURS.  BOTH THE UKMET AND AVIATION
MODELS WEAKEN OLGA TO A DEPRESSION OR LESS WITHIN 72 HOURS.  THE
SHIPS MODEL MAINTAINS A 55 KT STORM BY 72 HOURS...BUT I BELIEVE IT
DOES NOT HAVE A GOOD HANDLE ON THE SHEAR...WHILE THE GFDL BRINGS
OLGA DOWN TO 30 KT.  ALTHOUGH OLGAS OVERALL CIRCULATION IS STILL
LARGE...THE AREA COVERED BY STRONG WINDS IS RATHER SMALL...SO THE
MAXIMUM WINDS COULD DROP QUICKLY ONCE THE INNER CORE BEGINS TO
COLLAPSE.  THE OFFICIAL FORECAST CALLS FOR MORE WEAKENING THAN THE
PREVIOUS FORECAST...BUT IS NOT AS RAPID AS THE GLOBAL MODELS OR
GFDL.

AFTER COMPLETING A RELATIVELY LARGE CYCLONIC LOOP THIS AFTERNOON...
OLGA IS NOW EXECUTING A SECOND...MUCH TIGHTER LOOP.  THIS SUGGESTS
THAT THE BINARY INTERACTIONS WITH VORTICITY CENTERS IN ITS IMMEDIATE
ENVIRONMENT ARE ENDING.  THE NET EFFECT OF ALL THIS LOOPING IS AN
OFFICIALLY STATIONARY INITIAL MOTION.  THE TROPICAL CYCLONE IS
EMBEDDED WITHIN A LARGER-SCALE DEEP-LAYER CYCLONIC CIRCULATION THAT
IS PRETTY MUCH ISOLATED FROM THE MAIN BELT OF WESTERLIES.  THIS
LARGER CIRCULATION IS EXPECTED TO SHIFT SLOWLY SOUTHWESTWARD OVER
THE NEXT FEW DAYS...AND BRING OLGA WITH IT.  THERE IS NOW GOOD
AGREEMENT AMONG THE UKMET...AVIATION...AND GFDL MODELS.  THE
OFFICIAL TRACK FORECAST SHOWS THE SOUTHWESTWARD MOTION COMMENCING IN
A DAY OR SO...AND IS AGAIN FASTER THAN THE PREVIOUS OFFICIAL
FORECAST...BUT STILL SLOWER THAN THE GLOBAL MODEL CONSENSUS.

FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     28/0900Z 32.6N  55.8W    75 KTS
12HR VT     28/1800Z 32.5N  56.0W    70 KTS
24HR VT     29/0600Z 32.5N  56.0W    65 KTS
36HR VT     29/1800Z 31.0N  57.5W    60 KTS
48HR VT     30/0600Z 29.5N  59.5W    55 KTS
72HR VT     01/0600Z 28.0N  63.0W    45 KTS
 
 
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