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Tropical Depression EIGHT


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TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
1100 AM EDT WED SEP 13 2006
 
MORNING VISIBLE IMAGERY INDICATES THAT TROPICAL DEPRESSION EIGHT
REMAINS POORLY ORGANIZED...WITH THE CIRCULATION ELONGATED
WEST-SOUTHWEST TO EAST-NORTHEAST AND SEVERAL VORTICITY MAXIMA
ROTATING AROUND THE MEAN CENTER.  SCATTERED CONVECTIVE CLUSTERS ARE
PRESENT IN THE WESTERN SEMICIRCLE.  SATELLITE INTENSITY ESTIMATES
ARE 30 KT FROM ALL AGENCIES...AND THAT REMAINS THE INITIAL
INTENSITY.

THE INITIAL MOTION IS 270/15.  THE DEPRESSION IS SOUTH OF A
DEEP-LAYER RIDGE OVER THE EASTERN ATLANTIC...WHICH SHOULD KEEP THE
SYSTEM MOVING GENERALLY 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.  ONE EXCEPTION TO THIS IS
THE CANADIAN MODEL...WHICH IS A LEFT OUTLIER BRINGING THE CYCLONE
TO JUST NORTHEAST OF THE LEEWARD ISLANDS BY 120 HR.  THE NEW
FORECAST TRACK FOLLOWS THE MAJORITY OF THE GUIDANCE IN CALLING FOR
A NORTHWESTWARD MOTION BY 120 HR.  THE NEW FORECAST TRACK IS A
LITTLE TO THE LEFT OF THE MODEL CONSENSUS DUE TO A PAST TENDENCY OF
THE LARGE-SCALE MODELS TO MOVE TROPICAL CYCLONES TOO FAR NORTH IN
THIS SYNOPTIC PATTERN.

THE CURRENT BROAD AND DISORGANIZED STRUCTURE SUGGESTS THAT
SHORT-TERM INTENSIFICATION SHOULD BE SLOW.  THUS...THE INTENSITY
FORECAST TAKES 24 HR TO BRING THE DEPRESSION TO TROPICAL STORM
STRENGTH.  AFTER THAT...THE SYSTEM SHOULD STRENGTHEN AT A FASTER
RATE IN A LIGHT VERTICAL SHEAR ENVIRONMENT...AND IT IS FORECAST TO
BECOME A HURRICANE IN 72-96 HR.  THERE ARE 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 AT THIS TIME.  THE SECOND IS AN UPPER-LEVEL
TROUGH FORECAST BY THE LARGE-SCALE MODELS TO THE NORTH OR NORTHEAST
OF THE LESSER ANTILLES BY 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      13/1500Z 12.0N  28.5W    30 KT
 12HR VT     14/0000Z 12.2N  30.7W    30 KT
 24HR VT     14/1200Z 12.8N  34.0W    35 KT
 36HR VT     15/0000Z 13.8N  37.0W    40 KT
 48HR VT     15/1200Z 15.1N  39.6W    50 KT
 72HR VT     16/1200Z 18.0N  43.5W    60 KT
 96HR VT     17/1200Z 20.0N  46.5W    70 KT
120HR VT     18/1200Z 22.0N  49.5W    80 KT
 
$$
FORECASTER BEVEN
 
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