Tropical Depression TWELVE-E

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TROPICAL DEPRESSION TWELVE-E SPECIAL DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
1000 AM PDT TUE SEP 18 2007
 
VISIBLE SATELLITE IMAGERY INDICATES THAT THE AREA OF DISTURBED
WEATHER SOUTHWEST OF THE COAST OF MEXICO HAS BECOME BETTER
ORGANIZED...WITH CONVECTION DEVELOPING OVER THE LOW-LEVEL CENTER. 
SATELLITE INTENSITY ESTIMATES ARE 25 KT FROM TAFB AND SAB...AND A
QUIKSCAT OVERPASS NEAR 1330Z SUGGESTED MAXIMUM WINDS OF 25-30 KT. 
THE INITIAL INTENSITY IS SET TO 25 KT.

THE CENTER POSITION IS A LITTLE UNCERTAIN...WITH QUIKSCAT SUGGESTING
A POSITION SOMEWHAT TO THE SOUTHWEST OF MICROWAVE AND CONVENTIONAL
SATELLITE IMAGERY.  THIS YIELDS A SOMEWHAT UNCERTAIN MOTION OF
290/11.  THE DEPRESSION IS 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
AND HWRF MODELS SHOWING A SLOW EASTWARD MOTION.  THE FORECAST TRACK
CALLS FOR RECURVATURE AND DECELERATION DURING THE FORECAST
PERIOD...WITH A LITTLE MORE NORTHERLY MOTION THAN CALLED FOR BY THE
GFDL AND HWRF. 

THE CYCLONE IS CURRENTLY IN AN ENVIRONMENT OF LIGHT NORTHWESTERLY
VERTICAL WIND SHEAR.  THE LARGE-SCALE MODELS FORECAST THIS TO
CONTINUE FOR 48-72 HR...FOLLOWED BY A SIGNIFICANT INCREASE IN THE
SHEAR.  COMBINED WITH THE DEPRESSION MOVING OVER COOLER WATER AT
ABOUT 72 HR...THIS EVOLUTION WOULD SUGGEST GRADUAL STRENGTHENING
THROUGH 72 HR FOLLOWED BY WEAKENING.  THE INTENSITY FORECAST IS IN
BEST AGREEMENT WITH THE SHIPS MODEL.  THE GFDL CALLS FOR THE SYSTEM
TO REACH HURRICANE STRENGTH BEFORE WEAKENING...SO THERE IS A CHANCE
IT COULD BECOME STRONGER THAN FORECAST BEFORE THE SHEAR INCREASES.
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/1700Z 13.4N 107.9W    25 KT
 12HR VT     19/0000Z 13.9N 109.0W    30 KT
 24HR VT     19/1200Z 14.7N 111.2W    35 KT
 36HR VT     20/0000Z 15.5N 112.8W    40 KT
 48HR VT     20/1200Z 16.4N 114.1W    45 KT
 72HR VT     21/1200Z 18.5N 115.0W    50 KT
 96HR VT     22/1200Z 20.0N 114.5W    40 KT
120HR VT     23/1200Z 21.0N 113.0W    30 KT
 
$$
FORECASTER BEVEN
 
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