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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT SAT SEP 16 2000

AIR FORCE RECON IS HAVING DIFFICULTY CLOSING OFF A CENTER.  THUS THE
SYSTEM IS ON THE VERGE OF OPENING UP INTO A TROPICAL WAVE.  VISIBLE
SATELLITE PICTURES SHOW THE LOW-LEVEL CENTER...OR VORTICITY
MAXIMUM...MOVING WESTWARD OUT AHEAD OF THE MAIN AREA OF CONVECTION. 
THE RAPID WESTWARD MOVEMENT OF THIS CENTER IS RESULTING IN A LACK OF
DEFINITE WEST WINDS OVER THE SOUTHERN SEMICIRCLE.  HOWEVER SINCE THE
PLANE REPORTED TROPICAL STORM FORCE WINDS AT FLIGHT LEVEL OVER THE
NORTHERN PORTION OF THE SYSTEM...WE WILL HANG ON TO THE SYSTEM AS A
DEPRESSION FOR THIS ADVISORY AND KEEP THE TROPICAL STORM WATCHES FOR
THE NORTHERN LEEWARDS.  HOWEVER...IF THE CURRENT DISORGANIZING TREND
CONTINUES...WE MAY BE FORCED TO DISCONTINUE ADVISORIES LATER TODAY. 

RAWINSONDE DATA FROM GUADELOUPE SHOW MOSTLY EAST-NORTHEAST WINDS
FROM LOW LEVELS THROUGH 250 MB WITH SOME HIGHER-LEVEL WESTERLIES. 
SO IF THE LOW-LEVEL CENTER SLOWS DOWN...THE SHEAR MAY NOT BE SO
PROHIBITIVE AND THE SYSTEM COULD SURVIVE.  FOR NOW...I AM SHOWING NO
CHANGE IN STRENGTH THROUGH THE FORECAST PERIOD.

NOT MUCH CHANGE IS MADE TO THE TRACK FORECAST OR THE REASONING...
EXCEPT THAT THE FORWARD SPEED...15 KNOTS...IS SOMEWHAT FASTER THAN
BEFORE.  A MID-LEVEL ANTICYCLONE TO THE NORTH OF THE DEPRESSION IS
EXPECTED BUILD WESTWARD WITH THE TROPICAL CYCLONE...AND MAINTAIN A
MOSTLY WESTWARD STEERING FLOW.  THE OFFICIAL TRACK FORECAST IS VERY
SIMILAR TO THE GFDL GUIDANCE.

EVEN THOUGH THE SYSTEM IS DISORGANIZED...WINDS TO TROPICAL STORM
FORCE IN GUSTS WILL PROBABLY OCCUR OVER PORTIONS OF THE LEEWARD
ISLANDS LATER TODAY AND TONIGHT.
 
FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     16/1500Z 16.1N  57.3W    30 KTS
12HR VT     17/0000Z 16.2N  59.7W    30 KTS
24HR VT     17/1200Z 16.5N  63.0W    30 KTS
36HR VT     18/0000Z 16.8N  66.0W    30 KTS
48HR VT     18/1200Z 17.0N  69.0W    30 KTS
72HR VT     19/1200Z 17.5N  74.0W    30 KTS
 
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