Tropical Depression SEVENTEEN-E

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TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP172009
800 PM PDT TUE SEP 22 2009
 
SATELLITE IMAGERY INDICATES THAT THE BROAD AREA OF LOW PRESSURE
LOCATED SEVERAL HUNDRED MILES SOUTHWEST OF THE SOUTHERN TIP OF BAJA
CALIFORNIA HAS ACQUIRED SUFFICIENT CONVECTION ORGANIZATION TO BE
DESIGNATED AS A TROPICAL DEPRESSION...THE SEVENTEENTH OF THE
SEASON. THE DEPRESSION IS COMPRISED OF AN ELONGATED AND FAIRLY
SHAPELESS MASS OF CENTRAL CONVECTION...DISPLACED NORTHWEST OF THE
ESTIMATED CENTER DUE TO SOUTHEASTERLY SHEAR. DVORAK T-NUMBERS ARE
T 2.0 FROM BOTH TAFB AND SAB AND SERVE AS THE BASIS FOR SETTING THE
ADVISORY INTENSITY AT 30 KT. WITHIN 24 HOURS... SOUTHWESTERLY SHEAR
IS EXPECTED TO BEGIN INCREASING AND SHOULD BECOME PROHIBITIVELY
STRONG BY 48 HOURS. HOWEVER...PRIOR TO ENCOUNTERING THIS HIGH SHEAR
ENVIRONMENT...THE DEPRESSION HAS SOME OPPORTUNITY TO BECOME A
TROPICAL STORM. WEAKENING IS THEN FORECAST AFTER 36 HOURS...WITH
THE DEPRESSION FORECAST TO BECOME A REMNANT LOW BY 72 HOURS. THE
OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE SHIPS/LGEM GUIDANCE
AND DOES NOT CONSIDER THE GFDL/HWRF INTENSITY FORECASTS WHICH CALL
FOR THE DEPRESSION TO BECOME A HURRICANE. THESE FORECASTS APPEAR TO
BE UNREALISTIC..GIVEN THE STRONG SHEAR FORECAST BY THE GLOBAL
MODELS. 
 
THERE IS MORE UNCERTAINTY THAN NORMAL IN THE INITIAL MOTION...WHICH
IS ESTIMATED AT 320/08.  GLOBAL MODELS SHOW A BREAK IN THE
SUBTROPICAL RIDGE BETWEEN 115 WEST AND 120 WEST...WHICH SHOULD
STEER THE DEPRESSION ON A GENERAL NORTHWESTWARD COURSE FOR THE NEXT
24 HOURS. THEREAFTER...THE STRONG SHEAR FORECAST BY THE GLOBAL
MODELS SHOULD CAUSE A DECOUPLING OF THE CYCLONE...WITH THE LOW-
LEVEL CENTER EXPECTED TO TURN TOWARD THE WEST AT A REDUCED
FORWARD SPEED UNTIL DISSIPATION.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      23/0300Z 15.7N 115.7W    30 KT
 12HR VT     23/1200Z 16.4N 116.5W    35 KT
 24HR VT     24/0000Z 17.3N 117.5W    40 KT
 36HR VT     24/1200Z 17.6N 118.2W    35 KT
 48HR VT     25/0000Z 17.7N 119.0W    30 KT
 72HR VT     26/0000Z 17.8N 120.5W    20 KT...REMNANT LOW
 96HR VT     27/0000Z...DISSIPATED
 
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FORECASTER KIMBERLAIN
 
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