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Tropical Depression EIGHTEEN-E

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TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP182006
200 PM PDT THU OCT 26 2006
 
CONVENTIONAL SATELLITE IMAGERY DEPICTS DEVELOPING RAIN BANDS OVER
THE NORTHWEST QUADRANT AS WELL AS A VERY SMALL CENTRAL DENSE
OVERCAST FEATURE OVER THE CIRCULATION CENTER.  HOWEVER...THE
INITIAL INTENSITY IS HELD AT 30 KT DUE TO THE RATHER LIMITED AREAL
EXTENT OF DEEP CONVECTION.  THE GFDL AND THE SHIPS BOTH INDICATE
GRADUAL STRENGTHENING OVER THE NEXT 48 HOURS WITHIN LIGHT
SOUTHEASTERLY SHEAR...AND WITH A FORECAST MOTION OVER SEAS SURFACE
TEMPERATURES GREATER THAN 28C.  THE GFDL SUGGESTS A WEAKENING
BEYOND DAY 3 WHICH MIGHT BE DUE THERMODYNAMIC INFLUENCES.  THE
FORECAST INTENSITY IS SIMILAR TO THE PREVIOUS ADVISORY AND IS BASED
ON A BLEND OF THE AFOREMENTIONED MODELS. 
 
THE INITIAL MOTION IS ESTIMATED AT 290/6...WITHIN THE SOUTHWEST
PERIPHERY OF A MID- TROPOSPHERIC RIDGE EXTENDING WESTWARD FROM
CENTRAL MEXICO.  A MAJORITY OF THE LARGE SCALE MODELS...AND THE
GFDL...INDICATE A MID- TO UPPER LEVEL RIDGE BUILDING TO THE
NORTHWEST OF THE DEPRESSION DURING THE NEXT 24 TO 36 HOURS...
CAUSING THE SYSTEM TO TURN WEST-SOUTHWESTWARD WITH AN INCREASE IN
FORWARD SPEED.  IT SHOULD BE NOTED THAT THE 12Z MODEL RUNS FORECAST
A MORE PRONOUNCED BUILDING OF THE RIDGE COMPARED TO THE EARLIER
RUNS.  THROUGH THE LATTER PORTION OF THE FORECAST...THE MODELS
SUGGEST A WEAKENING TREND OF THE RIDGE IN RESPONSE TO A MAJOR
SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST.  THIS SHOULD CAUSE
A GRADUAL DECREASE IN MOTION WITH A TURN TO THE WEST-NORTHWEST...
TOWARD THE DEVELOPING WEAKNESS.  THE OFFICIAL FORECAST IS TO THE
LEFT OF AND FASTER THAN THE PREVIOUS FORECAST...AND IS BASED OFF OF
A CONSENSUS OF THE GFDL...ECMWF...AND THE GFS. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 17.0N 104.7W    30 KT
 12HR VT     27/0600Z 16.9N 105.7W    40 KT
 24HR VT     27/1800Z 16.6N 107.4W    45 KT
 36HR VT     28/0600Z 16.3N 109.4W    50 KT
 48HR VT     28/1800Z 16.1N 111.6W    55 KT
 72HR VT     29/1800Z 16.0N 115.0W    55 KT
 96HR VT     30/1800Z 16.5N 118.0W    50 KT
120HR VT     31/1800Z 17.0N 121.0W    45 KT
 
$$
FORECASTER ROBERTS/BEVEN
 
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