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TROPICAL STORM DALILA DISCUSSION NUMBER 21
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT WED JUL 25 2001
DALILA HAS STRENGTHENED SLIGHTLY AS THE CENTRAL DEEP CONVECTION HAS
BECOME BETTER ORGANIZED. THE VERTICAL SHEAR HAS WEAKENED ENOUGH TO
ALLOW FOR A MORE CIRCULAR OUTFLOW PATTERN TO DEVELOP DURING THE PAST
6 HOURS. THE INITIAL INTENSITY IS INCREASED TO 60 KT BASED ON
DVORAK SATELLITE INTENSITY ESTIMATES OF 65 KT...EMBEDDED CENTER
PATTERN...FROM TAFB AND 55 KT FROM SAB. THIS IS ALSO SUPPORTED BY
THE UW-CIMMS AMSU INTENSITY ESTIMATES SHOWING A PRESSURE DECREASE
DOWN TO 992 MB.
THE INITIAL MOTION ESTIMATE REMAINS AT 285/6. ALL OF THE DYNAMICAL
MODELS HAVE CONTINUED THE TREND OF TURNING DALILA SHARPLY TO THE
NORTHWEST FOR THE FIRST 24 HOURS AND THEN TAKING THE CYCLONE
WESTWARD AFTER THAT. THIS TREND HAS PERSISTED FOR SEVERAL MODEL
RUNS NOW AND IT HAS YET TO OCCUR. SURFACE ANALYSES INDICATE THE
RIDGE TO THE NORTH AND WEST OF DALILA HAS BUILT SOUTHWARD AS THE
REMNANT LOW THAT WAS ONCE TROPICAL STORM ERICK HAS WEAKENED AND
BECOME LESS DISTINCT. THE INCREASING EFFECT OF THE LOW- TO
MID-LEVEL RIDGING SHOULD KEEP THE CYCLONE ON A WEST-NORTHWEST OR
WESTWARD TRACK THROUGHOUT THE PERIOD. THE OFFICIAL FORECAST IS
BETWEEN THE DYNAMICAL MODELS CONSENSUS AND CLIPER...AND JUST A
LITTLE SOUTH OF THE PREVIOUS FORECAST TRACK.
ALTHOUGH DALILA IS MOVING OVER COOLER WATER...SSTS ARE STILL ABOVE
27C AND IT IS POSSIBLE THAT DALILA COULD REACH MINIMAL HURRICANE
INTENSITY AGAIN DURING THE NEXT 12 HOURS OR SO. HOWEVER...ALL OF
THE GLOBAL MODELS INDICATE ANOTHER SURGE OF STRONG UPPER-LEVEL
EASTERLY FLOW WILL AFFECT THE CYCLONE BY 24 HOURS...WHICH WILL
INCREASE THE VERTICAL SHEAR ONCE AGAIN. THE OFFICAL FORECAST SHOWS
SLOW WEAKENING THROUGH 24 HOURS AND THEN A SLIGHTLY FASTER DECREASE
IN INTENSITY AFTER THAT. THIS IS CONSISTENT WITH THE SHIPS
INTENSITY MODEL AND ALSO MAINTAINS CONTINUITY WITH THE PREVIOUS
INTENSITY FORECAST TREND.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 26/0300Z 19.4N 113.2W 60 KTS
12HR VT 26/1200Z 19.6N 114.2W 55 KTS
24HR VT 27/0000Z 19.9N 115.5W 50 KTS
36HR VT 27/1200Z 20.2N 116.8W 40 KTS
48HR VT 28/0000Z 20.5N 118.1W 30 KTS
72HR VT 29/0000Z 21.0N 120.5W 25 KTS...DISSIPATING
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