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Tropical Depression FOUR (Text)

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TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
500 AM EDT TUE AUG 14 2007
 
LATEST SATELLITE IMAGERY INDICATES THAT THERE HAS BEEN LITTLE
OVERALL CHANGE IN THE ORGANIZATION OR THE STRUCTURE OF THE
DEPRESSION.  THE LOW-LEVEL CIRCULATION IS STILL NOT WELL-DEFINED
AND IS ELONGATED EAST TO WEST WITH ALL OF THE DEEP CONVECTION
DISPLACED WEST OF THE ESTIMATED CENTER.  THE INITIAL INTENSITY
REMAINS 30 KT FOR THIS ADVISORY IN CONCURRENCE WITH DVORAK
ESTIMATES FROM BOTH TAFB AND SAB.  GLOBAL MODELS ALL INDICATE THAT
THE SHEAR WILL GRADUALLY RELAX OVER THE NEXT COUPLE OF DAYS AND AN
UPPER-LEVEL ANTICYCLONE WILL BUILD OVER THE CYCLONE.
THIS...COMBINED WITH INCREASINGLY WARMER WATERS ALONG THE FORECAST
TRACK...SHOULD CREATE A MORE FAVORABLE ENVIRONMENT FOR
INTENSIFICATION.  THE GFDL... HWRF...AND SHIPS MODELS ARE NOW
FORECASTING PEAK INTENSITIES OF 110 KT...104 KT...AND 92 KT
RESPECTIVELY.  HOWEVER...CONSIDERING THE PRESENT LACK OF
ORGANIZATION...THE OFFICIAL FORECAST STAYS NEAR THE LOWER END OF
THE AVAILABLE INTENSITY GUIDANCE AND IS PRACTICALLY UNCHANGED FROM
THE PREVIOUS ADVISORY. 
 
UNDER THE INFLUENCE OF A STRONG DEEP-LAYER RIDGE TO THE NORTH...THE
DEPRESSION CONTINUES TO MOVE RAPIDLY WESTWARD OR 270/18.  THIS
GENERAL MOTION IS LIKELY TO CONTINUE DURING THE NEXT DAY OR TWO. 
THEREAFTER...A WEAKNESS IN THE RIDGE OVER THE CENTRAL ATLANTIC
SHOULD CAUSE A GRADUAL TURN TOWARD THE WEST-NORTHWEST WITH A
REDUCTION IN FORWARD SPEED.  BY DAYS 4-5...MODELS BEGIN TO DIVERGE
DUE TO DIFFERING FORECASTS OF AN MID/UPPER-LEVEL CUTOFF LOW
EXPECTED TO FORM OFF THE SOUTHEASTERN UNITED STATES COAST.  THE
UKMET QUICKLY DISSIPATES THE LOW...ALLOWING MID-LEVEL RIDGING TO
BUILD OVER THE WESTERN ATLANTIC.  CONVERSELY...THE GFS SHOWS THE
MID/UPPER-LEVEL LOW REMAINING STATIONARY...PRODUCING A GAP IN THE
SUBTROPICAL RIDGE.  THE LATEST OFFICIAL FORECAST IS NUDGED TOWARD
THE MODEL CONSENSUS AND IS A LITTLE SOUTH OF...AND SLIGHTLY SLOWER
THAN...THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0900Z 12.0N  36.8W    30 KT
 12HR VT     14/1800Z 12.0N  39.3W    35 KT
 24HR VT     15/0600Z 12.1N  42.1W    40 KT
 36HR VT     15/1800Z 12.3N  45.0W    45 KT
 48HR VT     16/0600Z 12.7N  47.9W    55 KT
 72HR VT     17/0600Z 14.0N  53.5W    65 KT
 96HR VT     18/0600Z 16.0N  59.0W    80 KT
120HR VT     19/0600Z 18.5N  63.5W    90 KT
 
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