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Tropical Depression TWELVE (Text)

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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT WED SEP 03 2003
 
PREVIOUS DEEP CONVECTION HAS DISSIPATED AND MOVED EASTWARD AWAY FROM
THE LOW-LEVEL CENTER. SOME SMALLER CIRCULATIONS HAVE BEEN NOTED
MOVING CYCLONICALLY AROUND THE MEAN CENTER...BUT I HAVE OPTED TO
REMAIN CLOSE TO THE PREVIOUS ADVISORY LOCATION BASED ON NIGHTIME
VISIBLE AND INFRARED SATELLITE IMAGERY...AND NO APPARENT CHANGE IN
THE SURROUNDING WIND FIELD NOTED IN THE GULF BUOY OBSERVATIONS. THE
LAST RECON REPORT AROUND 03/2116Z INDICATED THAT THE PRESSURE HAD
DROPPED TO 1011 MB AND THAT PRESSURE WAS USED FOR THIS ADVISORY.

THE DEPRESSION HAS ESSENTIALLY BEEN STATIONARY FOR THE PAST 12 HOURS
OR SO AS THE CYCLONE REMAINS CAUGHT IN THE MID-LEVEL SUBTROPICAL
RIDGE AXIS THAT EXTENDS EAST-WEST ACROSS THE FLORIDA PENINSULA.
HOWEVER...A GRADUAL ACCELERATION TO THE NORTHEAST OR EAST-NORTHEAST
IS EXPECTED TO RESUME IN THE NEXT 12 HOURS OR SO AS A MID-LEVEL
TROUGH CURRENTLY OVER THE SOUTHERN PLAINS SHIFTS EASTWARD TO THE
SOUTHEASTERN U.S. AND SLOWLY PICKS UP TD-12. THE FORECAST TRACK IS
CLOSE TO THE PREVIOUS TRACK...BUT A LITTLE SLOWER AS THE RIDGE
BETWEEN TD-12 AND HURRICANE FABIAN IS EXPECTED TO STRENGTHEN AND
SLOW THE EASTWARD PROGRESS OF THE DEPRESSION. BY 72 HOURS...AFTER
FABIAN IS EXPECTED TO RAPIDLY ACCELERATE NORTHEASTWARD...THE RIDGE
BETWEEN THE TWO CYCLONES SHOULD WEAKEN AND ALLOW FOR TD-12 TO MOVE
MORE RAPIDLY NORTHEASTWARD OFF THE SOUTHEAST U.S. COAST. THIS
SCENARIO IS CLOSE TO A BLEND OF THE GFS AND THE GFDL MODELS.
 
THE DEPRESSION IS CURRENTLY UNDER MODERATE SOUTHWESTERLY UPPER-LEVEL
SHEAR. ALSO...WATER VAPOR IMAGERY INDICATES THAT MID-/UPPER-LEVEL
DRY AIR HAS BEEN PUNCHING INTO THE SYSTEM FROM THE SOUTH. HOWEVER
...MOISTURE FROM A LARGE THUNDERSTORM COMPLEX OVER THE YUCATAN MAY
GET DRAWN INTO THE SYSTEM IN ABOUT 12 TO 18 HOURS WHEN THE SHEAR IS
ALSO FORECAST TO WEAKEN SLIGHTLY. THIS MAY ALLOW CONVECTION TO
DEVELOP AND PERSIST NEAR THE LOW-LEVEL CENTER...AND ALSO ALLOW THE
DEPRESSION TO REACH TROPICAL STORM STATUS. HOWEVER...IT APPEARS
THAT IT WILL BE ROUGHLY 24 HOURS OR SO BEFORE THE DEPRESSION CAN
BECOMES "HENRI THE 8TH"...TROPICAL STORM OF THE SEASON.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      04/0300Z 27.5N  87.5W    25 KT
 12HR VT     04/1200Z 28.1N  86.3W    30 KT
 24HR VT     05/0000Z 28.5N  84.6W    35 KT
 36HR VT     05/1200Z 29.0N  82.8W    40 KT
 48HR VT     06/0000Z 29.3N  81.0W    40 KT
 72HR VT     07/0000Z 30.5N  78.0W    40 KT
 96HR VT     08/0000Z 33.0N  75.0W    30 KT...EXTRATROPICAL
120HR VT     09/0000Z 36.5N  68.5W    30 KT...EXTRATROPICAL
 
 
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