[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 060234
TCDAT4
TROPICAL DEPRESSION NINE DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI AUG 05 2005

TROPICAL DEPRESSION NINE HAS A LARGE AND WELL-DEFINED SWIRL OF LOW
CLOUDS THIS EVENING...BUT THERE IS NO ORGANIZED CONVECTION NEAR THE
CENTER AT THIS TIME.  THE CYCLONE IS OVER 26C-27C SEA SURFACE
TEMPERATURES...AND THE WEST-NORTHWESTWARD MOTION HAS TAKEN IT INTO
AN AREA OF WESTERLY VERTICAL SHEAR.  THIS COMBINATION HAS
INTERRUPTED DEVELOPMENT.  THE INITIAL INTENSITY IS REMAINS 25 KT
BASED ON SATELLITE INTENSITY ESTIMATES...ALONG WITH QUIKSCAT AND
SSM/I WINDS.

THE INITIAL MOTION IS 295/17.  THE DEPRESSION IS SOUTH OF A LOW/
MID-LEVEL RIDGE OVER THE EASTERN ATLANTIC.  OBSERVATIONS AND
LARGE-SCALE MODEL ANALYSES SHOW A WEAKNESS IN THIS RIDGE BETWEEN
50W-60W PARTLY ASSOCIATED WITH TROPICAL STORM HARVEY...AND THIS
WEAKNESS WILL NOT COMPLETELY FILL DURING THE NEXT FIVE DAYS.  IN
RESPONSE...THE CYCLONE SHOULD MOVE GENERALLY WEST-NORTHWESTWARD
WITH SOME SLOWING FOR ABOUT 72 HR...AND THEN POSSIBLY TURN
NORTHWESTWARD.  THE TRACK FORECAST GUIDANCE AGREES ON THE FIRST 2-3
DAYS OF MOTION AND THEN DIVERGES.  THE UKMET AND THE BAM MODELS
CALL FOR A CONTINUED WEST-NORTHWESTWARD MOTION AT 96-120 HR...WHILE
THE NOGAPS...LBAR...AND GFS ENSEMBLE MEAN CALL FOR A TURN TOWARD
THE NORTH.  THE OFFICIAL FORECAST WILL COMPROMISE BETWEEN THESE
EXTREMES...CALLING FOR A GRADUAL NORTHWESTWARD TURN IN BEST
AGREEMENT WITH THE CONSENSUS MODEL CONU.  THE FORECAST AFTER 72 HR
IS ALSO SLOWER THAN EARLIER IN LIGHT OF THE GUIDANCE SPREAD.

WATER VAPOR IMAGERY SHOWS A STRONG UPPER-LEVEL LOW NEAR 27N42W WITH
A TROUGH EXTENDING TO NEAR 19N44W.  THIS SYSTEM HAS CREATED
WESTERLY UPPER-LEVEL FLOW OVER THE DEPRESSION.  LARGE-SCALE MODELS
SUGGEST A SHEARING ENVIRONMENT COULD CONTINUE FOR 2-3 DAYS AS A
SERIES OF UPPER-LEVEL SHORTWAVE TROUGHS PASS NEAR OR NORTH OF THE
DEPRESSION.  THE SHIPS MODEL SLOWLY STRENGTHENS THE SYSTEM DESPITE
THE SHEAR AS IT MOVES GRADUALLY OVER WARMER SEA SURFACE
TEMPERATURES...AND THE INTENSITY FORECAST FOLLOWS THAT GUIDANCE.
HOWEVER...THERE IS A CHANCE THAT THE SYSTEM COULD DISSIPATE OR
DEGENERATE INTO A LOW PRESSURE AREA BEFORE CONDITIONS BECOME MORE
FAVORABLE....AS FORECAST BY THE GFDL AND GFS MODELS.

FORECASTER BEVEN


FORECAST POSITIONS AND MAX WINDS

INITIAL      06/0300Z 17.6N  40.6W    25 KT
 12HR VT     06/1200Z 18.5N  42.6W    25 KT
 24HR VT     07/0000Z 19.6N  44.9W    25 KT
 36HR VT     07/1200Z 20.6N  46.9W    30 KT
 48HR VT     08/0000Z 21.7N  49.0W    30 KT
 72HR VT     09/0000Z 23.5N  52.5W    35 KT
 96HR VT     10/0000Z 25.0N  55.0W    40 KT
120HR VT     11/0000Z 27.5N  56.5W    45 KT


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