Tropical Depression TWELVE-E

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TROPICAL DEPRESSION TWELVE-E DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
200 PM PDT TUE SEP 18 2007
 
SATELLITE IMAGERY INDICATES THAT TROPICAL DEPRESSION TWELVE-E IS
GETTING BETTER ORGANIZED...WITH A BAND OF CURVED CONVECTION FORMING
NEAR THE CENTER.  SATELLITE INTENSITY ESTIMATES ARE 30 KT FROM TAFB
AND SAB...SO THAT IS THE INITIAL INTENSITY FOR THIS ADVISORY. 
HOWEVER...THE ORGANIZATION HAS IMPROVED SINCE THE ESTIMATES WERE
MADE...AND THERE IS A CHANCE THIS INTENSITY IS A LITTLE
CONSERVATIVE.  WHILE THE SYSTEM REMAINS UNDER LIGHT NORTHWESTERLY
VERTICAL SHEAR...THE CIRRUS OUTFLOW IS IMPROVING EVEN IN THE
NORTHWEST QUADRANT.

THE INITIAL MOTION IS 295/10.  THE DEPRESSION REMAINS ON THE SOUTH
SIDE OF OF A MID-LEVEL RIDGE EXTENDING WESTWARD FROM NORTHERN
MEXICO.  THE DYNAMICAL MODELS FORECAST THIS RIDGE TO BREAK DURING
THE NEXT THREE DAYS AS A LARGE DEEP-LAYER LOW MOVES SOUTHWARD OVER
CALIFORNIA.  THIS SHOULD ALLOW THE DEPRESSION TO TURN NORTHWARD AND
THEN NORTHEASTWARD BY THE END OF THE FORECAST PERIOD.  HOWEVER...
THE LOW DOES NOT MOVE FAR ENOUGH SOUTH FOR ACCELERATION AFTER
RECURVATURE...WITH THE GFDL SHOWING LITTLE MOTION AND THE HWRF
MODEL SHOWING A SLOW EASTWARD MOTION.  THE FORECAST TRACK AGAIN
CALLS FOR RECURVATURE AND DECELERATION DURING THE FORECAST PERIOD.
IT IS SIMILAR TO THE PREVIOUS FORECAST FOR THE FIRST 72 HR AND THEN
SHIFTED A LITTLE TO THE NORTHWEST THEREAFTER.
 
THE LARGE-SCALE MODELS FORECAST THE CURRENT LIGHT SHEAR TO CONTINUE
FOR 48-72 HR...FOLLOWED BY A SIGNIFICANT INCREASE IN THE SHEAR. 
THIS...COMBINED WITH DRY AIR SEEN IN WATER VAPOR IMAGERY NORTHWEST
OF THE CYCLONE AND MOTION OVER COOLER WATER AT ABOUT 72 HR...
SUGGESTS GRADUAL STRENGTHENING THROUGH 72 HR FOLLOWED BY WEAKENING. 
NONE OF THE GUIDANCE CURRENTLY FORECASTS THE DEPRESSION TO BECOME A
HURRICANE...SO THE INTENSITY FORECAST WILL FOLLOW THAT IN CALLING
FOR A PEAK INTENSITY OF 55 KT.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/2100Z 13.8N 108.4W    30 KT
 12HR VT     19/0600Z 14.5N 110.1W    35 KT
 24HR VT     19/1800Z 15.4N 112.2W    40 KT
 36HR VT     20/0600Z 16.2N 113.7W    45 KT
 48HR VT     20/1800Z 17.1N 114.6W    50 KT
 72HR VT     21/1800Z 19.0N 115.0W    55 KT
 96HR VT     22/1800Z 20.5N 114.5W    45 KT
120HR VT     23/1800Z 21.5N 113.5W    30 KT
 
$$
FORECASTER BEVEN
 
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