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Tropical Storm DEAN


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TROPICAL STORM DEAN DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
500 AM EDT WED AUG 15 2007
 
THE CENTRAL CONVECTION ASSOCIATED WITH DEAN HAS MORE OF A BANDED
APPEARANCE THIS MORNING...ALTHOUGH THE BANDING IS NOT YET
WELL-DEFINED.  WHILE VERTICAL WIND SHEAR HAS DECREASED...IT MAY BE
THAT A COMBINATION OF DRY AIR SEEN IN WATER VAPOR IMAGERY NEAR THE
STORM AND INFLOW FROM OVER THE COOLER WATERS TO THE NORTH ARE
SLOWING AN INCREASE IN CONVECTIVE ORGANIZATION.  THE INITIAL
INTENSITY REMAINS 45 KT BASED ON CONTINUITY FROM THE EARLIER
QUIKSCAT DATA AND THE PREVIOUS ADVISORY.

THE INITIAL MOTION IS A SLIGHTLY UNCERTAIN 275/16...UNCERTAIN DUE TO
AMSU MICROWAVE DATA HINTING THAT THE CENTER IS A LITTLE SOUTH OF
THE ADVISORY POSITION.  WATER VAPOR IMAGERY INDICATES THAT DEAN IS
ON THE SOUTH SIDE OF A DEEP-LAYER RIDGE... WITH A LARGE
MID/UPPER-LEVEL TROUGH COVERING THE ATLANTIC AND CARIBBEAN BETWEEN
64W-77W.  THE LARGE-SCALE MODELS SUGGEST THAT THE TROUGH SHOULD
GRADUALLY FILL DURING THE FORECAST PERIOD...WITH RIDGING PERSISTING
NORTH OF DEAN.  THIS SHOULD RESULT IN A GENERAL WESTWARD TO
WEST-NORTHWESTWARD MOTION.  THERE HAVE BEEN SOME CHANGES IN THE
MODEL GUIDANCE...AS THE CANADIAN AND ECMWF MODELS HAVE SHIFTED FROM
A WEST-NORTHWESTWARD TRACK TOWARD THE BAHAMAS TO A MORE WESTWARD
MOTION THROUGH THE CARIBBEAN.  THE UKMET CONTINUES TO CALL FOR A
GENERAL WESTWARD MOTION...WHILE THE GFS CALLS FOR A WEST-
NORTHWESTWARD MOTION NEAR THE END OF THE FORECAST PERIOD.  THE
NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK THROUGH 72
HR...THEN SHIFTED A LITTLE WEST OF THE PREVIOUS TRACK THEREAFTER
BASED ON THE OVERALL CHANGE IN THE ENVELOPE OF GUIDANCE.  THE NEW
TRACK IS IN BEST AGREEMENT WITH...BUT A LITTLE SLOWER THAN...THE
GFS.

DEAN SHOULD ENCOUNTER WARMER SEA SURFACE TEMPERATURES ALONG THE
FORECAST TRACK...AND THE VERTICAL SHEAR IS FORECAST TO BE LIGHT
DURING THE FORECAST PERIOD.  THE INTENSITY GUIDANCE CALLS FOR
STEADY STRENGTHENING...AND SO DOES THE INTENSITY FORECAST IN BEST
AGREEMENT WITH THE ICON CONSENSUS.  GIVEN THE FAVORABLE UPPER-LEVEL
WINDS AND WARM WATER...THERE IS A POSSIBILITY THAT DEAN COULD BE
NOTABLY STRONGER THAN FORECAST BY THE END OF THE FORECAST PERIOD.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/0900Z 12.2N  44.2W    45 KT
 12HR VT     15/1800Z 12.4N  46.6W    50 KT
 24HR VT     16/0600Z 12.8N  50.1W    55 KT
 36HR VT     16/1800Z 13.2N  53.7W    60 KT
 48HR VT     17/0600Z 13.8N  57.1W    70 KT
 72HR VT     18/0600Z 15.0N  63.0W    80 KT
 96HR VT     19/0600Z 16.0N  68.5W    90 KT
120HR VT     20/0600Z 17.5N  74.0W   100 KT
 
$$
FORECASTER BEVEN
 
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