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Tropical Storm DARBY (Text)

ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM DARBY DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP052010
800 PM PDT WED JUN 23 2010

THE RAPID INTENSIFICATION THAT DARBY WAS UNDERGOING EARLIER SEEMS TO
HAVE SLOWED OR STOPPED...AS THERE HAS BEEN NO RECENT HINT OF AN EYE
IN VISIBLE OR INFRARED IMAGERY AND MUCH OF THE OUTER BANDING
ASSOCIATED WITH DARBY HAS DISSIPATED.  WHY THIS IS OCCURRING IS NOT
OBVIOUS...AS THERE ARE NO ANALYSES THAT SHOW SIGNIFICANT VERTICAL
WIND SHEAR AFFECTING THE STORM.  IT IS POSSIBLE THAT EASTERLY
UPPER-LEVEL WINDS ARE UNDERCUTTING THE WELL-DEFINED ANTICYCLONIC
OUTFLOW.  SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 55
KT...AND THAT IS THE INITIAL INTENSITY FOR THIS ADVISORY.

THE INITIAL MOTION REMAINS 285/10.  DARBY IS SOUTH OF A LOW/MID-
LEVEL RIDGE OVER MEXICO.  THE LARGE-SCALE MODELS FORECAST THE RIDGE
TO WEAKEN AS A DISTURBANCE OVER THE NORTHWESTERN CARIBBEAN SEA
MOVES TOWARDS THE YUCATAN PENINSULA AND THE GULF OF MEXICO.  THIS
SHOULD LEAVE DARBY IN AN AREA OF LIGHT STEERING CURRENTS BY 72-96
HR...WITH THE LOW-LEVEL FLOW TRYING TO MOVE THE CYCLONE EASTWARD
AND THE MID-LEVEL FLOW TRYING TO MOVE IT WESTWARD.  THERE IS A
LARGE SPREAD IN THE DYNAMICAL MODELS AFTER 72 HR...WHICH IS ANOTHER
SIGN THAT THE CYCLONE IS LIKELY TO MOVE SLOWLY.  THE NEW FORECAST
TRACK IS SIMILAR TO THE PREVIOUS TRACK...CALLING FOR A WEST-
NORTHWESTWARD MOTION AND DECELERATION FOR 48 HR OR SO...FOLLOWED BY
A NORTHWARD TURN AT A SLOW FORWARD SPEED.  THE NEW TRACK IS IN BEST
AGREEMENT WITH THE FLORIDA STATE SUPERENSEMBLE.

DESPITE THE CURRENT TRENDS...THE INTENSITY GUIDANCE FORECASTS DARBY
TO STRENGTHEN FURTHER...WITH THE SHIPS AND LGEM MODELS SHOWING A
PEAK INTENSITY OF 80 KT IN ABOUT 48 HR AND THE SHIPS RAPID
INTENSIFICATION INDEX SHOWING A 40 PERCENT CHANCE OF 30 KT
STRENGTHENING DURING THE NEXT 24 HR.  AFTER THAT...INCREASING
EASTERLY WIND SHEAR IS LIKELY TO ARREST DEVELOPMENT AND BEGIN A
WEAKENING TREND.  THE NEW INTENSITY FORECAST FOLLOWS THE TREND OF
THE PREVIOUS FORECAST BUT AT SOMEWHAT LOWER INTENSITIES BASED ON
CURRENT TRENDS AND THE FORECAST SHEAR.  THE NEW FORECAST IS
STRONGER THAN ALL THE GUIDANCE AT 96 AND 120 HR.  IT SHOULD BE
NOTED THAT THE GFS...UKMET...NOGAPS...AND ECMWF MODELS SHOW DARBY
SHEARING APART AFTER 72 HR...WITH THE LOW-LEVEL CENTER MOVING
EASTWARD AND THE MID-LEVEL CENTER MOVING WESTWARD.  SHOULD THIS
HAPPEN THE CYCLONE WOULD WEAKEN MUCH FASTER THAN CURRENTLY
FORECAST.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/0300Z 12.3N  97.0W    55 KT
 12HR VT     24/1200Z 12.7N  98.3W    65 KT
 24HR VT     25/0000Z 13.1N  99.8W    75 KT
 36HR VT     25/1200Z 13.4N 100.9W    80 KT
 48HR VT     26/0000Z 13.6N 101.7W    85 KT
 72HR VT     27/0000Z 14.0N 102.5W    85 KT
 96HR VT     28/0000Z 14.5N 102.5W    80 KT
120HR VT     29/0000Z 15.0N 102.5W    65 KT
 
$$
FORECASTER BEVEN
 
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