Tropical Depression TWENTY-ONE-E

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TROPICAL DEPRESSION TWENTY-ONE-E SPECIAL DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP212006
1000 PM PDT MON NOV 13 2006
 
OVER THE PAST COUPLE OF HOURS...DEEP CONVECTION HAS INCREASED NEAR
THE ESTIMATED CENTER OF THE LOW PRESSURE SYSTEM SEVERAL HUNDRED
MILES SOUTH OF MANZANILLO MEXICO AND BANDING FEATURES ARE STARTING
TO BECOME MORE EVIDENT.  THEREFORE THE SYSTEM IS BEING DESIGNATED
AS A TROPICAL CYCLONE AND A SPECIAL ADVISORY IS BEING ISSUED AT
THIS TIME.  VERTICAL SHEAR IS CURRENTLY LIGHT OVER THE AREA AND
GRADUAL STRENGTHENING IS LIKELY OVER THE NEXT DAY OR TWO. 
THEREAFTER...WE EXPECT THE SYSTEM TO COME UNDER THE INFLUENCE OF
STRONG WEST-SOUTHWESTERLY UPPER-LEVEL WINDS WHICH WOULD REVERSE THE
INTENSIFICATION PROCESS.  THE NHC WIND SPEED FORECAST IS BELOW THE
SHIPS GUIDANCE SINCE WE DO NOT BELIEVE THAT MODEL IS DIAGNOSING
STRONG ENOUGH SHEAR IN THE LATTER PART OF THE FORECAST PERIOD.

INITIAL MOTION IS ABOUT 300/7.  STEERING CURRENTS ARE FORECAST TO
COLLAPSE AS HIGH PRESSURE WEAKENS TO THE NORTH OF THE TROPICAL
CYCLONE.  GLOBAL MODELS SUCH AS THE GFS APPEAR TO HAVE BOTH A POOR
INITIALIZATION AND AN UNREALISTIC EVOLUTION OF THE SYSTEM AS THEY
SEEM TO OVEREMPHASIZE A CYCLONIC CIRCULATION TO THE WEST AND
SOUTHWEST OF THE TROPICAL CYCLONE.  AT THE MOMENT...THE COURSE OF
LEAST REGRET IS TO FORECAST A SLOW...AND GENERALLY NORTHWESTWARD...
MOTION THROUGH MOST OF THE FORECAST PERIOD.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0500Z 12.9N 104.5W    25 KT
 12HR VT     14/1200Z 13.4N 105.2W    35 KT
 24HR VT     15/0000Z 14.0N 105.8W    40 KT
 36HR VT     15/1200Z 14.5N 106.2W    45 KT
 48HR VT     16/0000Z 15.0N 106.6W    45 KT
 72HR VT     17/0000Z 16.0N 107.0W    40 KT
 96HR VT     18/0000Z 17.0N 107.5W    35 KT
120HR VT     19/0000Z 17.5N 108.0W    30 KT
 
$$
FORECASTER PASCH/BROWN
 
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