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Tropical Depression EIGHTEEN


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TROPICAL DEPRESSION EIGHTEEN DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 18 2005
 
THE RECONAISSANCE AIRCRAFT THAT WAS EN ROUTE TO TROPICAL STORM
PHILIPPE WAS DIVERTED TO THE DEPRESSION...AND WE VERY MUCH
APPRECIATE THE LAST MINUTE FLEXIBILITY OF THE AIRCREW.  WHEN THEY
FIRST GOT TO THE DEPRESSION...THEY DIDN'T FIND MUCH...INCLUDING
ONLY 5 KT OF WEST WIND AND A CENTER SOUTHWEST OF THE DEEP
CONVECTION.  HOWEVER...ON THEIR SECOND PASS THROUGH THEY FOUND THAT
THE CENTER HAD MIGRATED OR REDEVELOPED CLOSER TO THE CONVECTION...
WHICH IS NOW TAKING ON A SLIGHTLY MORE BANDED APPEARANCE ON THE
FIRST FEW IMAGES AFTER THE SATELLITE ECLIPSE.  THESE OBSERVATIONS
SUGGEST THAT THE DEPRESSION IS BECOMING BETTER ORGANIZED.  THE PEAK
FLIGHT-LEVEL WINDS WERE 36 KT...WHICH SUPPORTS AN INITIAL INTENSITY
ESTIMATE OF 25 KT.
 
THE AIRCRAFT DATA REQUIRE A RELOCATION OF THE CENTER TO THE SOUTH
AND WEST OF THE PREVIOUS TRACK...AND THIS RESULTS IN A SLIGHT
SOUTHWARD SHIFT OF THE OFFICIAL FORECAST. HOWEVER...THE BASIC TRACK
REASONING REMAINS THE SAME. THE DEPRESSION IS EXPECTED TO MOVE
WEST-NORTHWESTWARD FOR THE NEXT COUPLE OF DAYS TOWARD A WEAKNESS IN
THE SUBTROPICAL RIDGE JUST EAST OF FLORIDA. AFTER THAT...HIGH
PRESSURE OVER TEXAS AND THE WESTERN GULF SHOULD TURN THE DEPRESSION
WESTWARD.  THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE GFS
AND GFDL GUIDANCE.  THE UKMET IS FARTHER SOUTH...TAKING THE CYCLONE
ACROSS CENTRAL AND WESTERN CUBA.  THE CANADIAN MODEL IS ALSO SOUTH
OF ITS PREVIOUS TRACK...TAKING THE CENTER JUST SOUTH OF KEY WEST.

UPPER-LEVEL LOW PRESSURE IS CENTERED OVER CENTRAL CUBA...AND THIS
LOW IS PRODUCING SOME SOUTHERLY SHEAR OVER THE DEPRESSION.  THIS
SHOULD LIMIT INTENSIFICATION IN THE SHORT TERM...HOWEVER...THIS LOW
IS FORECAST BY ALL THE GLOBAL MODELS TO WEAKEN AND BE REPLACED BY A
NARROW RIDGE OF HIGH PRESSURE OVER THE NEXT TWO TO THREE DAYS. 
THIS UPPER PATTERN...COUPLED WITH VERY WARM SEA SURFACE
TEMPERATURES ALONG THE PATH OF THE CYCLONE...WOULD FAVOR MORE RAPID
DEVELOPMENT AS LONG AS THE CYCLONE AVOIDS THE LAND MASS OF CUBA. 
THE GFDL IS NOT NEARLY AS AGRESSIVE AS IT WAS EARLIER TODAY...NOT
MAKING THE SYSTEM A HURRICANE UNTIL IT IS WELL INTO THE GULF OF
MEXICO.  THE OFFICIAL FORECAST IS A LITTLE SLOWER THAN THE PREVIOUS
ADVISORY IN BRINGING THE SYSTEM TO HURRICANE STRENGTH AND FOLLOWS A
BLEND OF THE SHIPS AND GFDL GUIDANCE. 
 
FORECASTER FRANKLIN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/0900Z 21.7N  71.2W    25 KT
 12HR VT     18/1800Z 22.2N  73.0W    30 KT
 24HR VT     19/0600Z 22.8N  75.3W    35 KT
 36HR VT     19/1800Z 23.4N  77.5W    45 KT
 48HR VT     20/0600Z 23.8N  80.0W    55 KT
 72HR VT     21/0600Z 24.0N  84.5W    65 KT
 96HR VT     22/0600Z 24.0N  89.5W    75 KT
120HR VT     23/0600Z 24.0N  93.5W    80 KT
 
 
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