Tropical Depression EIGHT

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TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
500 PM AST WED SEP 13 2006
 
SATELLITE IMAGERY THIS AFTERNOON INDICATES THAT TROPICAL DEPRESSION
EIGHT IS SLOWLY BECOMING BETTER ORGANIZED.  A CONVECTIVE BAND HAS
FORMED IN THE NORTHWESTERN QUADRANT...ALTHOUGH THE BAND IS MORE
THAN 100 N MI FROM THE CENTER IN MOST AREAS.  THE OVERALL
CIRCULATION IS MORE CIRCULAR AND BETTER DEFINED THAN 6 HR AGO. 
SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB...AND 30 KT FROM
SAB AND AFWA.  THE INITIAL INTENSITY REMAINS 30 KT.  IT SHOULD BE
NOTED THAT THE INITIAL POSITION IS SOUTH OF THE SATELLITE FIXES...
AND THE CENTER MAY BE TRYING TO RE-FORM FARTHER NORTH CLOSER TO THE
CONVECTION.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 275/16...WITH A POSSIBLE
FASTER MOTION OVER THE PAST FEW HOURS.  THE DEPRESSION REMAINS
SOUTH OF A DEEP-LAYER RIDGE OVER THE EASTERN ATLANTIC...WHICH
SHOULD KEEP THE SYSTEM MOVING QUICKLY WESTWARD FOR 24 HR OR SO. 
AFTER THAT...THE LARGE-SCALE MODELS FORECAST THE CYCLONE TO
GRADUALLY TURN WEST-NORTHWESTWARD AND THEN NORTHWESTWARD TOWARD A
WEAKNESS IN THE RIDGE NORTHEAST OF THE LESSER ANTILLES.  THE UKMET
AND THE NOGAPS FORECAST MORE RIDGING NORTH OF THE DEPRESSION THAN
THEIR PREVIOUS RUNS...AND THEY TURN THE CYCLONE TO SOMEWHAT TO THE
LEFT AFTER 96 HR.  THIS IS REFLECTED IN THE NEW FORECAST TRACK. 
THE CANADIAN REMAINS A LEFT OUTLIER....ALTHOUGH IT HAS SHIFTED TO
THE RIGHT OF ITS PREVIOUS TRACK.  THE GFS...GFDL...AND ECMWF ARE
SIMILAR TO THEIR PREVIOUS RUNS...WITH THE GFDL FASTER THAN THE
OTHER MODELS AFTER 72 HR.  THE NEW FORECAST TRACK IS FASTER THAN
THE PREVIOUS TRACK DURING THE FIRST 24 HR...THEN IS SLOWER THAN THE
PREVIOUS TRACK AFTER 72 HR.  IT LIES NEAR THE SOUTH EDGE OF THE
MAIN CLUSTER OF GUIDANCE.
 
THE BROAD STRUCTURE SUGGESTS THAT SHORT-TERM INTENSIFICATION SHOULD
BE SLOW.  THIS IS REFLECTED IN THE FIRST 24 HR OF THE INTENSITY
FORECAST.  THE SYSTEM SHOULD THEN STRENGTHEN AT A FASTER RATE IN A
LIGHT VERTICAL SHEAR ENVIRONMENT...AND IT IS FORECAST TO BECOME A
HURRICANE IN ABOUT 72 HR.  THE INTENSITY FORECAST IS IN BEST
AGREEMENT WITH THE GFDL.  THERE REMAIN TWO COMPLICATING FACTORS IN
THE INTENSITY FORECAST.  THE FIRST IS DRY AIR PRESENT NORTH AND
WEST OF THE CYCLONE.  HOW MUCH OF THIS AIR WILL BE ENTRAINED INTO
THE SYSTEM IS UNCLEAR.  THE SECOND IS AN UPPER-LEVEL TROUGH
FORECAST BY THE LARGE-SCALE MODELS TO THE NORTH OR NORTHEAST OF THE
LESSER ANTILLES BY 96-120 HR.  WHILE THE MODELS AGREE THE TROUGH
WILL EXIST...THEY DO NOT AGREE ON THE LOCATION OR ON THE POSSIBLE
IMPACT TO THE CYCLONE.
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/2100Z 12.7N  30.7W    30 KT
 12HR VT     14/0600Z 12.9N  33.3W    35 KT
 24HR VT     14/1800Z 13.6N  36.4W    40 KT
 36HR VT     15/0600Z 14.7N  39.0W    50 KT
 48HR VT     15/1800Z 16.1N  41.1W    60 KT
 72HR VT     16/1800Z 18.5N  44.0W    70 KT
 96HR VT     17/1800Z 20.5N  46.5W    80 KT
120HR VT     18/1800Z 22.0N  49.5W    85 KT
 
$$
FORECASTER BEVEN
 
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