Tropical Storm DARBY

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TROPICAL STORM DARBY DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP052010
800 PM PDT SUN JUN 27 2010

DARBY REMAINS IN AN ENVIRONMENT OF STRONG NORTHEASTERLY SHEAR...AND 
THE LOW-LEVEL CENTER IS LOCATED NEAR THE NORTHEASTERN EDGE OF A MASS
OF DISORGANIZED DEEP CONVECTION.  USING AN AVERAGE OF DVORAK FINAL
T-NUMBERS AND CURRENT INTENSITY NUMBERS FROM BOTH TAFB AND SAB
LEADS TO A WIND SPEED ESTIMATE OF 40 KT FOR THIS ADVISORY.  GLOBAL
MODEL FORECASTS INDICATE THAT THE SHEAR AFFECTING DARBY WILL BECOME
EVEN STRONGER...IN EXCESS OF 30 KT...OVER THE NEXT DAY OR TWO. 
THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE AND
IS ALSO A BLEND OF THE SHIPS AND LGEM GUIDANCE.  EVEN THOUGH DARBY
WILL REMAIN OVER WARM WATERS...IT IS LIKELY TO BECOME QUITE WEAK
AND DEGENERATE INTO A REMNANT LOW BY THE TIME IT NEARS THE SOUTH
COAST OF MEXICO.

THE INITIAL MOTION IS AROUND 070/3.  THE DOMINANT STEERING MECHANISM
FOR THIS STORM REMAINS A BROAD AREA OF SOUTHWESTERLY LOW- TO
MID-LEVEL FLOW ON THE SOUTHERN SIDE OF THE LARGE GYRE ASSOCIATED
WITH ATLANTIC BASIN TROPICAL CYCLONE ALEX.  THE CONSENSUS OF THE
TRACK GUIDANCE CALLS FOR THE WEAKENING DARBY TO CONTINUE
EAST-NORTHEASTWARD WITH A SLIGHT INCREASE IN FORWARD SPEED DURING
THE NEXT 24-48 HOURS.  THIS OFFICIAL TRACK FORECAST IS QUITE
SIMILAR TO THE PREVIOUS ONE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/0300Z 13.9N 102.1W    40 KT
 12HR VT     28/1200Z 14.2N 101.5W    35 KT
 24HR VT     29/0000Z 14.5N 100.5W    30 KT
 36HR VT     29/1200Z 14.9N  99.3W    25 KT...POST-TROP/REMNT LOW
 48HR VT     30/0000Z 15.3N  98.0W    20 KT...POST-TROP/REMNT LOW
 72HR VT     01/0000Z...DISSIPATED
 
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FORECASTER PASCH
 
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