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TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   6
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT THU AUG 10 2000
 
THERE HAS BEEN LITTLE CHANGE IN TROPICAL DEPRESSION FOUR DURING THE
DAY...AS SPORADIC PUFFS OF CONVECTION ERUPT IN THE LOW CLOUD SWIRL
AND QUICKLY DIE.  THE MAXIMUM WINDS REMAIN AT 30 KT IN THIS
ADVISORY.  HOWEVER...SINCE THE CENTRAL PRESSURE HAS RISEN A LITTLE
AND THE TIGHT CORE SEEN YESTERDAY HAS DISSIPATED...IT MIGHT BE A
LITTLE WEAKER.

THE CYCLONE MOVED 090/5 DURING THE DAY...ALTHOUGH RECENT SATELLITE
IMAGERY SUGGESTS A POSSIBLY SLOWER MOTION.  THE SYNOPTIC SCENARIO IS
BECOMING COMPLEX.  LARGE-SCALE MODELS INDICATE THE STRONG UPPER
LEVEL TROUGH OVER THE EASTERN U.S. WILL TRIGGER SOME KIND OF SURFACE
DEVELOPMENT EITHER OVER THE MID-ATLANTIC STATES OR JUST OFF THE
COAST.  THE NOGAPS EVEN USES T.D. 4 TO TRIGGER THIS DEVELOPMENT. IF
THE BAROCLINIC LOW FORMS...THE LOW LEVEL FLOW SHOULD BE STRONG
ENOUGH TO WHISK T.D. 4 OFF TO THE NORTHEAST.  A COMPLICATING FACTOR
IS THE DISTURBANCE EAST-NORTHEAST OF T.D. 4.  IT IS LARGER THAN THE
DEPRESSION AND IT COULD KEEP T.D. 4 ON A MORE SOUTHERLY AND SLOWER
TRACK...ESPECIALLY IF IT DEVELOPS INTO A TROPICAL CYCLONE.  THE
OFFICIAL FORECAST IS A COMPROMISE BETWEEN A FASTER TRACK CLOSER TO
THE BAROCLINIC LOW AND A SLOWER TRACK CAUSED BY THE DISTURBANCE...
AND IS VERY CLOSE TO THE BAMS AND BAMM.
 
LARGE-SCALE MODELS FORECAST THAT THE CURRENTLY EASTERLY SHEAR WILL
DIMINISH IN THE NEXT 12 HR OR SO.  SHOULD THIS HAPPEN...IT COULD
ALLOW THE DEPRESSION TO STRENGTHEN.  ONE POSSIBILITY TO WATCH FOR IS
THAT TROPICAL CYCLONES MOVING AHEAD OF BAROCLINIC SYSTEMS SOMETIMES
STRENGTHEN CONSIDERABLY...ESPECIALLY WHEN IN THE WARM SECTOR...OVER
WARM WATER...AND EAST OF THE STRONG SHEAR IN THE JET STREAM CORE. 
T.D. 4 (AND THE DISTURBANCE) MAY WIND UP IN THIS SITUATION.  THE
OTHER POSSIBILITY IS THAT THIS SMALL AND POORLY ORGANIZED CYCLONE
MAY DISSIPATE BEFORE IT HAS A CHANCE TO STRENGTHEN.  THE INTENSITY
FORECAST IS A COMPROMISE BETWEEN THESE EXTREMES.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     10/2100Z 28.8N  78.1W    30 KTS
12HR VT     11/0600Z 28.8N  77.2W    30 KTS
24HR VT     11/1800Z 29.0N  75.5W    35 KTS
36HR VT     12/0600Z 29.8N  73.7W    40 KTS
48HR VT     12/1800Z 31.0N  71.5W    45 KTS
72HR VT     13/1800Z 36.5N  66.5W    45 KTS
 
 
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