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TROPICAL STORM JOYCE DISCUSSION NUMBER  16
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT FRI SEP 29 2000
 
HERE WE HAVE YET ANOTHER EXAMPLE OF OUR LACK OF UNDERSTANDING OF
TROPICAL CYCLONE INTENSITY CHANGE.  MORNING VISUAL IMAGES REVEAL AN
EXPOSED LOW-LEVEL CENTER TO THE WEST OF A SMALL AND RAGGED-LOOKING
AREA OF DEEP CONVECTION...SO THE CIRCULATION HAS BECOME DECOUPLED IN
THE VERTICAL.  IT IS NOT CLEAR WHY SUCH A SHEARING ENVIRONMENT
EXISTS SINCE WATER VAPOR ANIMATION DOES NOT SHOW STRONG UPPER-LEVEL
WINDS ACROSS THE CENTER OF JOYCE.  SINCE THE SYSTEM HAS BECOME SO
DISORGANIZED IT IS BEING DOWNGRADED TO A TROPICAL STORM.  THE
QUESTION THEN IS...WILL JOYCE RE-STRENGTHEN?  OUR BEST OBJECTIVE
INTENSITY FORECAST GUIDANCE...THE STATISTICAL/DYNAMICAL MODEL
SHIPS...SAYS YES.  BECAUSE OF THE GUIDANCE...AND THE FACT THAT THE
ENVIRONMENT AHEAD OF THE STORM STILL APPEARS TO BE FAVORABLE...THE
OFFICIAL FORECAST CALLS FOR AN EVENTUAL RE-INTENSIFICATION OF JOYCE
BUT NOT QUITE AS MUCH AS THE SHIPS MODEL CALLS FOR.
 
THE SOUTHWARD COMPONENT OF MOTION APPEARS TO BE GONE....INITIAL
HEADING IS NOW 270/12.  THE TRACK FORECAST IS ADJUSTED ONLY SLIGHTLY
NORTH OF THE PREVIOUS ONE.  OBJECTIVE TRACK PREDICTIONS ARE SPREAD
BETWEEN THE MORE NORTHWEST AND SLOWER MOTION SHOWN BY THE
GFDL...KEEPING JOYCE EAST OF THE LESSER ANTILLES AT 72 HOURS...TO
THE U.K. MET OFFICE MODEL WHICH MOVES THE SYSTEM INTO THE EXTREME
EASTERN CARIBBEAN.  SINCE THE GLOBAL MODELS SHOW A MID-LEVEL RIDGE
TO THE NORTH OF JOYCE THROUGH THE PERIOD...AND BECAUSE OF THE U.K.
MET SOLUTION...THE OFFICIAL TRACK FAVORS THE MORE WESTWARD OPTION.  
 
FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     29/1500Z 10.5N  49.2W    60 KTS
12HR VT     30/0000Z 10.5N  50.8W    60 KTS
24HR VT     30/1200Z 11.0N  53.0W    60 KTS
36HR VT     01/0000Z 11.5N  55.0W    65 KTS
48HR VT     01/1200Z 12.5N  57.0W    70 KTS
72HR VT     02/1200Z 15.0N  60.5W    80 KTS
 
 
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