Tropical Depression SIX

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TROPICAL DEPRESSION SIX DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT MON JUL 21 2003
 
THE LOW LEVEL CENTER IS NOT WELL DEFINED.  THE INITIAL MOTION
ESTIMATE IS 280/20 BASED MAINLY ON CONTINUITY.  THE GFS AND OTHER
DYNAMICAL MODELS SHOW A WEAKNESS IN THE SUBTROPICAL RIDGE IN THE
VICINITY OF FLORIDA.  A SHORT WAVE TROUGH IS FORECAST TO AMPLIFY
THIS WEAKNESS AND SHIFT IT A LITTLE WESTWARD.  THE UKMET HAS THE
WEAKNESS MOVING MUCH FURTHER EAST THAN THE GFS AND THIS RESULTS IN
THE UKMET MOVING THE SYSTEM NORTHWARD JUST EAST OF FLORIDA BY DAY
4.  THE GFS LOSES THE CIRCULATION AFTER DAY 3 BUT SUGGESTS A TRACK
MUCH FURTHER SOUTH AND WEST.  THE NOGAPS IS IN BETWEEN WITH A TRACK
TO THE NORTHEAST GULF OF MEXICO BY DAY 5.  THE OFFICIAL FORECAST IS
A COMPROMISE INTO THE EASTERN GULF BY DAY 5 AND IS SIMILAR TO THE
PREVIOUS ADVISORY FORECAST.  SO THERE IS A RATHER LARGE UNCERTAINTY
ABOUT THE TRACK AFTER DAY 3.

RECENT SATELLITE IMAGERY SHOWS A NOT VERY IMPRESSIVE CONVECTIVE
PATTERN TO GO ALONG WITH THE POORLY DEFINED CENTER.  AN AIRCRAFT
WILL INVESTIGATE THIS AFTERNOON TO DETERMINE THE EXACT LOCATION AND
INTENSITY.  A RECENT QUIKSCAT SHOWS WINDS NEAR 45 KNOTS BUT THE
INTENSITY WILL BE KEPT AT 30 KNOTS UNTIL RECONNAISSANCE DATA
CONFIRMS THE WIND SPEED.  MEANWHILE WATCHES AND WARNINGS ARE IN
PLACE FOR MOST OF THE CENTRAL LESSER ANTILLES IN THE EVENT THAT
THE WINDS ARE ACTUALLY ABOVE STORM STRENGTH.  EXCEPT FOR THE PURE
STATISTICAL SHIFOR MODEL WHICH HAS 80 KNOTS ON DAY 5...NONE OF THE
OTHER GUIDANCE FORECASTS MORE THAN ABOUT 50 KNOTS WITH A FAIR
AMOUNT OF VERTICAL SHEAR ANTICIPATED THROUGH DAY 5.  THE OFFICIAL
WIND SPEED FORECAST GOES TO 55 KNOTS AT DAY 3 THROUGH 5 WHICH IS A
LITTLE LESS THAN THE PREVIOUS ADVISORY.  

FAST MOVING SYSTEMS SUCH AS THIS ONE ARE A CHALLENGE IN THAT THERE
MAY NOT BE A CLOSED SURFACE CIRCULATION AND YET THE WINDS CAN BE
TROPICAL STORM FORCE.  THIS WAS THE CASE WITH CLAUDETTE MOVING
THROUGH THE ISLANDS AND MAY BE THE CASE WITH THIS DEPRESSION.

FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      21/1500Z 14.2N  58.8W    30 KT
 12HR VT     22/0000Z 14.8N  62.0W    35 KT
 24HR VT     22/1200Z 15.9N  66.4W    40 KT
 36HR VT     23/0000Z 17.3N  70.1W    45 KT
 48HR VT     23/1200Z 19.0N  74.0W    50 KT
 72HR VT     24/1200Z 22.0N  80.0W    55 KT
 96HR VT     25/1200Z 25.0N  84.0W    55 KT
120HR VT     26/1200Z 28.0N  86.0W    55 KT
 
 
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