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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT THU OCT 22 1998
 
ALTHOUGH TWO CONVECTIVE BANDS ARE SEEN ON THE WESTERN SIDE OF THE
TD...THE SYSTEM RETAINS AN OTHERWISE RATHER AMORPHOUS STRUCTURE AT
THIS POINT.  CENTER POSITION ESTIMATES REMAIN QUITE UNCERTAIN.  A
SHIP NEAR 12N 76W REPORTED EAST WINDS AT 12Z...BUT THE ACCURACY OF
THEIR WIND DIRECTION IS SOMEWHAT IN QUESTION ACCORDING TO THE MARINE
PREDICTION CENTER .  IF THE OBSERVATION IS VALID...THEN THE CENTER
OF CIRCULATION IS NOW LOCATED TO THE SE OF THE PREVIOUS ESTIMATES. 
THE REQUIRES SOME SOUTHEASTWARD RELOCATION OF THE CENTER POSITION...
AND IMPLIES LITTLE OR NO MOTION.  THE MOTION...STRUCTURE AND
INTENSITY SHOULD BE BETTER KNOWN AFTER THE HURRICANE HUNTERS ARRIVE
THERE THIS AFTERNOON.
 
THE 00Z NOGAPS AND 06Z AVN AND GFDL INDICATE THAT AFTER THE STRONG
500 MB SHORT-WAVE TROUGH PASSES BY TO THE NORTH...A RESIDUAL TROUGH
HANGS BACK NEAR THE U.S. SOUTHEAST COAST.  THIS WOULD ALLOW FOR SOME
NORTHWARD COMPONENT LATER IN THE FORECAST PERIOD.  IN CONTRAST...AT
850 MB...A LARGE ANTICYCLONE IS FORECAST TO PERSIST TO THE
NW...GIVING LOW LEVEL EASTERLIES.  IN COMBINATION...THIS
DISTRIBUTION YIELDS SOME SHEAR AND A LIGHT STEERING CURRENT TO THE
NW ON AVERAGE FOR THE NEXT FEW DAYS.  THIS IS THE NHC FORECAST.  ALL
AVAILABLE TRACK MODEL GUIDANCE ALSO SHOWS A NW HEADING.
 
AT UPPER LEVELS...THERE IS A COL LOCATED JUST NORTH OF THE TD...A
LITTLE SOUTH OF JAMAICA.  THE MODELS SHOW A MORE FAVORABLE
ENVIRONMENT DEVELOPING OVER THE CARIBBEAN DURING THE NEXT DAY OR
TWO.  BY THREE DAYS...HOWEVER...THE GFDL SHIFTS THE CENTER OF THE
200 MB ANTICYCLONE TO THE BAY OF CAMPECHE AND SHOWS A TROUGH OVER
THE NW CARIBBEAN.  THAT PATTERN WOULD NOT BE SO CONDUCIVE FOR
STRENGTHENING.

THE SLOW AND UNCERTAIN MOVEMENT ALLOWS/REQUIRES SOME DELAY IN
ISSUING WATCHES AND WARNINGS.
 
RAPPAPORT
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     22/1500Z 12.0N  78.0W    30 KTS
12HR VT     23/0000Z 12.4N  78.5W    40 KTS
24HR VT     23/1200Z 13.2N  79.4W    50 KTS
36HR VT     24/0000Z 13.8N  79.8W    60 KTS
48HR VT     24/1200Z 14.7N  80.3W    65 KTS
72HR VT     25/1200Z 16.5N  81.0W    70 KTS
 
 
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