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TROPICAL DEPRESSION THREE DISCUSSION NUMBER   1
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT WED AUG 18 1999

RECONNAISSANCE AND SURFACE OBSERVATIONS SHOW THAT A CLOSED
CIRCULATION HAS FORMED OVER THE BAY OF CAMPECHE.  THEREFORE
ADVISORIES ARE BEING INITIATED.

INITIAL MOTION IS HIGHLY UNCERTAIN BECAUSE THE SYSTEM IS STILL IN
THE DEVELOPING STAGE AND PREVIOUS CENTER FIXES SHOW A LOT OF
SCATTER.  MY BEST ESTIMATE IS WEST-NORTHWEST NEAR 7 KNOTS AT THIS
TIME.  THE NCEP GLOBAL MODEL SHOWS A RETROGRESSION OF THE MID-
TROPOSPHERIC RIDGE OVER THE SOUTH-CENTRAL UNITED STATES...WITH A
WEAKNESS EXTENDING NORTHEASTWARD FROM THE SOUTHWEST GULF TO A
DEVELOPING TROUGH OVER THE EASTERN UNITED STATES.  THIS COMPLICATES
THE TRACK FORECAST AND LEAVES OPEN THE POSSIBILITY THAT THE TROPICAL
CYCLONE COULD REMAIN OVER THE SOUTHWEST GULF FOR THE NEXT FEW
DAYS...DUE TO WEAK STEERING CURRENTS.  THIS IS SHOWN IN THE OFFICIAL
FORECAST AS WELL.

THE DEPRESSION IS CURRENTLY EXPERIENCE SOME WEST-SOUTHWESTERLY
SHEARING DUE TO AN UPPER-LEVEL TROUGH OVER THE EXTREME WESTERN GULF. 
THERE IS ALSO AN UPPER-LEVEL CYCLONE CURRENTLY LOCATED OVER THE
NORTH-CENTRAL GULF WHICH COULD BE IMPARTING SOME SHEAR.  EVEN THOUGH
THE SHEAR IS A NEGATIVE FACTOR FOR STRENGTHENING... THE ULTIMATE
EFFECT OF THE WEAK UPPER TROUGH ADJACENT TO THE DEPRESSION MAY BE TO
SPIN UP THE TROPICAL CYCLONE...AS SUGGESTED BY SOME RECENT RESEARCH. 
THE GLOBAL MODEL FORECAST SHOWS THESE UPPER-LEVEL CYCLONIC FEATURES
BECOMING MOSTLY INDISTINCT...WITH ANTICYCLONIC FLOW DEVELOPING OVER
THE AREA IN 2-3 DAYS.  THE OFFICIAL INTENSITY FORECAST SHOWS LITTLE
CHANGE IN STRENGTH EARLY IN THE PERIOD FOLLOWED BY SOME MODEST
INTENSIFICATION.  THIS ASSUMES THAT THE SYSTEM WILL REMAIN OVER
WATER THROUGHOUT THE PERIOD.

PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/2100Z 20.1N  93.7W    30 KTS
12HR VT     19/0600Z 20.2N  94.2W    30 KTS
24HR VT     19/1800Z 20.5N  95.0W    30 KTS
36HR VT     20/0600Z 20.7N  95.5W    35 KTS
48HR VT     20/1800Z 21.0N  96.0W    40 KTS
72HR VT     21/1800Z 21.5N  97.0W    50 KTS
 
 
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