Tropical Depression EIGHTEEN-E

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TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP182006
800 AM PDT THU OCT 26 2006
 
VISIBLE IMAGERY THIS MORNING SHOWS THAT THE AREA OF DISTURBED
WEATHER THAT HAS BEEN SOUTH OF THE COAST OF MEXICO FOR THE PAST TWO
DAYS IS NOW ORGANIZED ENOUGH TO BE DESIGNATED A TROPICAL
DEPRESSION.  THE CYCLONE HAS A SMALL AREA OF CENTRAL CONVECTION...
WITH WELL-DEFINED OUTER BANDS IN ALL QUADRANTS EXCEPT THE SOUTH. 
SATELLITE INTENSITY ESTIMATES ARE 30 KT FROM TAFB AND SAB...AND
THAT IS THE INITIAL INTENSITY. 
 
THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/8.  THE DEPRESSION IS
ON THE SOUTHWEST SIDE OF A MID/UPPER-LEVEL RIDGE CENTERED OVER
MEXICO.  LARGE-SCALE MODELS ALL AGREE THAT THIS RIDGE SHOULD BUILD
WESTWARD DURING THE NEXT 72 HR...WHICH SHOULD STEER THE DEPRESSION
ON A GENERALLY WESTWARD TRACK.  BY 96 HR...A SHORTWAVE TROUGH
MOVING TOWARD CALIFORNIA SHOULD WEAKEN THE RIDGE...LEAVING THE
DEPRESSION IN WEAK STEERING CURRENTS.  THE MODELS FORECAST THE
RIDGE TO RE-BUILD WEST OR WEST-NORTHWEST OF THE CYCLONE AFTER 96
HR...LEAVING THE CYCLONE ON THE WEST SIDE OF THE WEAKNESS AND
TURNING SOUTHWESTWARD.  THE FORECAST TRACK AFTER 72 HR IS SOMEWHAT
LOW CONFIDENCE...AS THERE IS A CHANCE THE CYCLONE COULD TURN
NORTHWARD INTO THE WEAKNESS IN THE RIDGE.

THE DEPRESSION IS CURRENTLY IN AN ENVIRONMENT OF LIGHT SOUTHEASTERLY
SHEAR...AND THE LARGE-SCALE MODELS FORECAST A LIGHT SHEAR
ENVIRONMENT TO PERSIST THROUGH 72 HR.  THE INTENSITY FORECAST CALLS
FOR STEADY SLOW STRENGTHENING...ALTHOUGH DUE TO THE SMALL INNER
CORE THERE IS A CHANCE IT COULD STRENGTHEN FASTER.  AFTER 72 HR...
THE MODELS DIVERGE ON THE AMOUNT OF SHEAR CAUSED BY THE SHORTWAVE
TROUGH.  THE GFS KEEPS ENOUGH UPPER-LEVEL RIDGING BETWEEN THE
DEPRESSION AND THE TROUGH TO KEEP THE SHEAR LIGHT.  ON THE OTHER
HAND...THE ECMWF AND NOGAPS FORECAST 20-25 KT OF NORTHWESTERLY
SHEAR...AND THE UKMET FORECASTS A VERY UNFAVORABLE 40-60 KT OF
NORTHWESTERLY SHEAR.  THE INTENSITY FORECAST WILL LEAN ON THE
ECMWF/NOGAPS SOLUTIONS TO FORECAST A SLOW WEAKENING AFTER 72 HR.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/1500Z 16.8N 104.2W    30 KT
 12HR VT     27/0000Z 17.1N 105.5W    35 KT
 24HR VT     27/1200Z 17.1N 107.1W    40 KT
 36HR VT     28/0000Z 17.1N 108.5W    45 KT
 48HR VT     28/1200Z 17.1N 110.0W    50 KT
 72HR VT     29/1200Z 17.0N 112.5W    60 KT
 96HR VT     30/1200Z 17.0N 113.5W    55 KT
120HR VT     31/1200Z 16.5N 114.5W    50 KT
 
$$
FORECASTER BEVEN
 
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