Tropical Depression SIXTEEN

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TROPICAL DEPRESSION SIXTEEN DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL162007
1100 PM EDT SAT OCT 27 2007
 
THE AREA OF LOW PRESSURE IN THE CARIBBEAN SEA HAS DEVELOPED ENOUGH
ORGANIZED CONVECTION TO BE CLASSIFIED AS A TROPICAL
DEPRESSION...WITH A LARGE CONVECTIVE MASS TO THE EAST AND NORTHEAST
OF THE PARTLY EXPOSED LOW-LEVEL CENTER.  SATELLITE INTENSITY
ESTIMATES ARE 30 KT FROM TAFB AND 25 KT FROM SAB...WHILE QUIKSCAT
DATA SHOWED NO RELIABLE WINDS HIGHER THAN 30 KT.  BASED ON
THIS...THE INITIAL INTENSITY IS SET AT 30 KT.  
 
THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 290/6.  THE LARGE
CYCLONIC ENVELOPE OF THE DEPRESSION IS LOCATED SOUTH OF A
LOW/MID-LEVEL RIDGE OVER THE WESTERN ATLANTIC...WITH AN UPPER-LEVEL
LOW OVER HAITI AND SURFACE TROUGHS OVER THE NORTHWESTERN CARIBBEAN
AND GULF OF MEXICO.  THE LARGE-SCALE MODELS GENERALLY FORECAST THE
ATLANTIC RIDGE TO GRADUALLY WEAKEN...WITH A MID/UPPER-LEVEL
SHORTWAVE TROUGH MOVING INTO THE SOUTHEASTERN UNITED STATES BY
96-120 HR.  THE TRACK GUIDANCE RESPONDS TO THIS EVOLUTION WITH A
RANGE OF POSSIBILITIES.  THE UKMET KEEPS THE SYSTEM SOUTH OF CUBA
BY 120 HR...WHILE THE NOGAPS FORECASTS IT TO REACH THE SOUTHEASTERN
GULF OF MEXICO BY THAT TIME.  THE GFS AND ECMWF FORECAST THE
CYCLONE TO TURN NORTHWARD BY 72-96 HR...THEN EITHER RECURVE OR
RE-FORM NORTHEASTWARD INTO THE NORTHERN BAHAMAS.  THE GFDL AND THE
HWRF CALL FOR A TRACK ACROSS HAITI AND THE CENTRAL BAHAMAS INTO THE
ATLANTIC.  THE TRACK FORECAST IS FURTHER COMPLICATED BY THE
GFS...ECMWF...AND NOGAPS SHOWING THE SEPARATION OF THE LOW-LEVEL
AND MID-LEVEL CENTERS BY 96-120 HR DUE TO SHEAR.  THE TRACK
FORECAST IS DOWN THE MIDDLE OF THIS SPREAD...WITH A NORTHWESTWARD
MOTION THROUGH 72 HR FOLLOWED BY A SLOW RECURVATURE INTO THE
WESTERLIES.  IT IS IN BEST AGREEMENT WITH THE GFS AND ECMWF.
 
THE COMBINATION OF THE LARGE SIZE OF THE DEPRESSION AND VERTICAL
WIND SHEAR FROM THE UPPER-LEVEL LOW SHOULD SLOW DEVELOPMENT DURING
THE FIRST 36 HR OR SO.  AFTER THAT...THE LARGE-SCALE MODELS BUILD A
LARGE UPPER-LEVEL ANTICYCLONE OVER THE WESTERN CARIBBEAN THAT COULD
PRODUCE A MORE FAVORABLE ENVIRONMENT FOR STRENGTHENING...IF THE
CYCLONE IS UNDER IT RATHER THAN NORTH OF IT AS CURRENTLY FORECAST. 
THE GFDL AND HWRF MAKE THE SYSTEM A HURRICANE OVER THE ATLANTIC
DESPITE STRONG SHEAR.  DUE TO THE UNCERTAINTY...THE INTENSITY
FORECAST CALLS FOR GRADUALLY STRENGTHENING THROUGH 72 HR...BELOW
THAT OF THE SHIPS...GFDL..AND HWRF.  AFTER 72 HR...LITTLE CHANGE IN
STRENGTH IS FORECAST DUE TO A COMBINATION OF LAND INTERACTION AND
INCREASING SHEAR ALONG THE FORECAST TRACK.

BOTH THE TRACK AND INTENSITY FORECASTS HAVE GREATER THAN NORMAL
UNCERTAINTY AT THIS TIME.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/0300Z 15.9N  71.5W    30 KT
 12HR VT     28/1200Z 16.6N  72.6W    35 KT
 24HR VT     29/0000Z 17.7N  74.2W    40 KT
 36HR VT     29/1200Z 18.8N  76.0W    45 KT
 48HR VT     30/0000Z 19.6N  77.6W    50 KT
 72HR VT     31/0000Z 21.0N  80.0W    60 KT
 96HR VT     01/0000Z 22.5N  80.0W    60 KT...INLAND
120HR VT     02/0000Z 25.0N  78.5W    60 KT
 
$$
FORECASTER BEVEN
 
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