Tropical Depression EIGHTEEN-E

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TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP182006
800 AM PDT FRI OCT 27 2006
 
LATE-NIGHT SHORTWAVE INFRARED AND MORNING VISIBLE IMAGERY SHOW THAT
THE CENTER OF THE TROPICAL DEPRESSION HAS BECOME EXPOSED ABOUT 90 N
MI SOUTHEAST OF THE REMAINING CONVECTION.  THE REASON FOR THIS IS
UNCLEAR...AS SHEAR ANALYSES FROM CIMSS AT THE UNIVERSITY OF
WISCONSIN SHOW ONLY 10-15 KT OF EASTERLY SHEAR OVER THE SYSTEM. 
WATER VAPOR IMAGERY SHOWS MID/UPPER-LEVEL DRY AIR NEAR THE
CYCLONE...AND PERHAPS THIS HAS HELPED DRY THE SYSTEM UP.  THE
INITIAL INTENSITY REMAINS 25 KT.

AS BEST AS CAN BE DETERMINED...THE CENTER MOVED ALMOST DUE SOUTH
DURING THE NIGHT...WHICH REQUIRES A RE-LOCATION FROM THE LAST
ADVISORY.  VISIBLE IMAGERY INDICATES SOME WESTWARD COMPONENT TO THE
MOTION...SO THE INITIAL MOTION IS AN UNCERTAIN 225/4.  LARGE-SCALE
MODELS AGREE THAT THE SYSTEM SHOULD TURN WEST-SOUTHWESTWARD DURING
THE NEXT 24 HOURS TO THE SOUTH OF OF A WESTWARD-BUILDING LOW/
MID-LEVEL RIDGE.  AFTER 24 HOURS...THE SYSTEM SHOULD MOVE GENERALLY
WESTWARD...WITH THE BAM MODELS SHOWING A WEST-NORTHWESTWARD MOTION
AFTER 48 HOURS...AND THE GLOBAL MODELS A WEST-SOUTHWESTWARD MOTION. 
THE NEW FORECAST TRACK IS SHIFTED WELL SOUTH OF THE PREVIOUS TRACK
BASED ON THE RE-LOCATION AND IS IN BEST AGREEMENT WITH THE GFDL.
 
THE PARTING OF THE CENTER AND THE CONVECTION REQUIRES A MAJOR CHANGE
IN THE INTENSITY FORECAST PHILOSOPHY.  ONLY THE SHIPS MODEL NOW
CALLS FOR PROLONGED STRENGTHENING...WITH THE OTHER AVAILABLE
INTENSITY GUIDANCE DISSIPATING THE SYSTEM BEFORE DAY 5.  THE
INTENSITY FORECAST NOW CALLS FOR THE SYSTEM TO PERSIST AS A WEAK
DEPRESSION FOR 72 HR...FOLLOWED BY WEAKENING TO A REMNANT LOW AND
DISSIPATION.  IF THE CONVECTION DOES NOT RE-DEVELOP NEAR THE
CENTER...THE CYCLONE WILL LIKELY DISSIPATE FASTER THAN CURRENTLY
FORECAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/1500Z 15.8N 105.2W    25 KT
 12HR VT     28/0000Z 15.5N 106.2W    25 KT
 24HR VT     28/1200Z 15.0N 108.0W    25 KT
 36HR VT     29/0000Z 14.7N 110.2W    25 KT
 48HR VT     29/1200Z 14.5N 112.3W    25 KT
 72HR VT     30/1200Z 14.5N 116.0W    25 KT...DISSIPATING
 96HR VT     31/1200Z 14.5N 120.0W    20 KT...REMNANT LOW
120HR VT     01/1200Z...DISSIPATED
 
$$
FORECASTER BEVEN
 
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