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TROPICAL STORM DALILA DISCUSSION NUMBER  20
NATIONAL WEATHER SERVICE MIAMI FL
2 PM PDT WED JUL 25 2001
 
VERTICAL SHEAR HAS CONTINUED TO DECREASE OVER DALILA...AND AS A
RESULT THE CYCLONE HAS CHANGED FROM A SHEAR PATTERN TO A CURVED
BAND PATTERN.  INDEED...THERE IS CONVECTION NOW TRYING TO WRAP
AROUND THE EASTERN SIDE OF THE CENTER.  SATELLITE INTENSITY
ESTIMATES ARE UNCHANGED FROM 6 HR AGO...SO THE INITIAL INTENSITY
REMAINS 55 KT.  IT IS NOTABLE THAT A QUIKSCAT OVERPASS AT 1312Z
REPORTED A 50 KT WIND...ALTHOUGH THIS WAS LIKELY RAIN CONTAMINATED.

THE INITIAL MOTION IS 285/6.  THE SYNOPTIC PATTERN AND FORECAST
PHILOSOPHY REMAIN UNCHANGED FROM THE PREVIOUS PACKAGE...WITH
DALILA LIKELY TO REMAIN ON A SLOW WEST-NORTHWESTWARD TRACK
THROUGH THE FORECAST PERIOD.  THE OFFICIAL FORECAST IS LITTLE
CHANGED FROM THE PREVIOUS PACKAGE AND IS IN BEST AGREEMENT WITH
NHC91 AND CLIPER.  IT SHOULD BE NOTED THAT WHILE THE BAM MODELS...
THE AVN...AND LBAR ALSO CALL FOR A GENERAL WEST-NORTHWESTWARD
MOTION...THEY ALL MOVE THE CYCLONE NORTHWESTWARD FOR THE FIRST
12 HR...WHICH DOES NOT APPEAR TO BE REALISTIC.
 
IF DALILA WERE OVER WARM ENOUGH WATER...THE DECREASED SHEAR WOULD
LIKELY ALLOW INTENSIFICATION.  INDEED...SOME SLIGHT STRENGTHENING
IS INDICATED BY THE SHIPS MODEL DURING THE FIRST 24 HR.  HOWEVER...
DALILA IS MOVING SLOWLY BUT STEADILY OVER COLDER WATER WHICH
SHOULD OFFSET THE EFFECTS OF THE REDUCED SHEAR.  THE INTENSITY
FORECAST IS THE SAME AS THE PREVIOUS PACKAGE...CALLING FOR A
SLOW WEAKENING THROUGHOUT THE FORECAST PERIOD.
 
THE QUIKSCAT PASS SUGGESTED TROPICAL STORM WINDS MAY EXTEND OUTWARD
UP TO 120 N MI TO THE SOUTHWEST OF THE CENTER.  HOWEVER...THE
VELOCITIES IN THIS AREA ARE SUSPECT DUE TO RAIN CONTAMINATION. NON-
RAIN-CONTAMINATED IN OTHER PARTS OF THE STORM SUGGEST THAT TROPICAL
STORM WINDS EXTEND OUT ABOUT 60 N MI...AND THAT WILL BE THE RADIUS
FOR THIS PACKAGE.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     25/2100Z 19.3N 112.6W    55 KTS
12HR VT     26/0600Z 19.6N 113.6W    50 KTS
24HR VT     26/1800Z 20.0N 114.9W    45 KTS
36HR VT     27/0600Z 20.4N 116.3W    35 KTS
48HR VT     27/1800Z 20.8N 117.7W    30 KTS
72HR VT     28/1800Z 21.5N 120.0W    25 KTS...DISSIPATING
 
 
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