000
WTPZ45 KNHC 270859
TCDEP5
TROPICAL STORM DARBY DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP052010
200 AM PDT SUN JUN 27 2010
 
DEEP CONVECTION ASSOCIATED WITH DARBY HAS BEEN BURSTING
INTERMITTENTLY THIS MORNING...BUT IS DISPLACED TO THE WEST OF THE
CIRCULATION CENTER.  UW-CIMSS SHEAR PRODUCT INDICATES 30 KT OF
EASTERLY SHEAR AFFECTING THE OUTFLOW OVER THE EASTERN HALF
OF THE CYCLONE.  THIS STRONG UPPER LEVEL FLOW IS ASSOCIATED WITH
THE OUTFLOW PATTERN OF TROPICAL STORM ALEX.  THE INITIAL INTENSITY
IS BASED ON A FEW INTENSITY ESTIMATES FROM CIMSS...AN AMSU ESTIMATE
OF 38 KT...A SATELLITE CONSENSUS MEASUREMENT OF 53 KT...AND
CONSTRAINED BY RULES...DVORAK SATELLITE ESTIMATES OF 66 KT AND 55
KT FROM TAFB AND SAB RESPECTIVELY.  BASED ON THESE DATA...THE
INITIAL INTENSITY IS LOWERED TO 50 KT.  THE SHIPS
MODEL...LGEM...AND FSU SUPERENSEMBLE ALL SUGGEST THAT THE EASTERLY
SHEAR AFFECTING DARBY WILL INCREASE THROUGH THE PERIOD...RESULTING
IN A CONTINUED WEAKENING TREND.  THE INTENSITY FORECAST FOLLOWS
SUIT AND IS BASED ON A BLEND OF THE AFOREMENTIONED MODELS REDUCING
DARBY TO A REMNANT LOW SWIRL OF CLOUDS IN 3 DAYS OR LESS.
 
INITIAL MOTION IS ESTIMATED AT 270/3...WITHIN THE LIGHT EASTERLY LOW
TO MID-LEVEL FLOW GENERATED BY A RIDGE EXTENDING TO THE NORTH OF
DARBY FROM CENTRAL MEXICO.  SINCE DARBY IS EXPECTED TO WEAKEN
CONSIDERABLY DURING THE NEXT COUPLE OF DAYS...THE DECAYING CYCLONE
SHOULD MAKE A TURN NORTHEASTWARD AROUND THE 24 HR PERIOD IN
RESPONSE TO THE RATHER LARGE LOW-LEVEL CIRCULATION OF TROPICAL
STORM ALEX CURRENTLY MOVING OVER YUCATAN.  THE OFFICIAL NHC
FORECAST IS CLOSE TO THE PREVIOUS FORECAST BUT A LITTLE SLOWER ON
THE TURN TO THE NORTHEAST...AND HEDGES TOWARD THE TVCN MODEL
CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0900Z 13.5N 103.3W    50 KT
 12HR VT     27/1800Z 13.5N 103.4W    40 KT
 24HR VT     28/0600Z 13.9N 103.0W    35 KT
 36HR VT     28/1800Z 14.2N 102.5W    25 KT
 48HR VT     29/0600Z 14.5N 101.9W    25 KT
 72HR VT     30/0600Z 14.9N 100.9W    20 KT...POST-TROP/REMNT LOW
 96HR VT     01/0600Z...DISSIPATED
 
$$
FORECASTER ROBERTS/STEWART