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TROPICAL STORM DALILA DISCUSSION NUMBER  17
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT TUE JUL 24 2001
 
DALILA HAS WEAKENED BACK TO A TROPICAL STORM DURING THE PAST 6 HOURS 
EVEN THOUGH DEEP CONVECTION HAS RE-DEVELOPED OVER THE LOW-LEVEL 
CENTER.  A 24/2010Z TRMM OVERPASS STILL INDICATED AN INTACT EYEWALL 
IN THE LOW-LEVELS... BUT THE MID/UPPER-LEVEL CIRCULATION WAS TILED 
TO THE SOUTHWEST.  THE INITIAL INTENSITY OF 60 KT IS BASED ON DVORAK 
INTENSITY ESTIMATES RANGING FROM 55 KT TO 65 KT FROM THE VARIOUS 
SATELLITE AGENCIES.  OUTFLOW IS FAIR IN THE WEST SEMICIRCLE AND POOR 
ELSEWHERE DUE TO EASTERLY SHEAR.

THE CENTER OF DALILA IS CURRENTLY PASSING OVER SOCORRO ISLAND.  THE 
INITIAL MOTION ESTIMATE IS 280/8. THERE IS NO SIGNIFICANT CHANGE TO 
THE PREVIOUS FORECAST TRACK PHILOSOPHY.  ALL OF THE MODEL GUIDANCE 
REMAINS TIGHTLY CLUSTERED ABOUT A GENERAL WEST-NORTHWEST TRACK 
BETWEEN 280 AND 295 DEGREES.  THE OFFICIAL FORECAST TRACK IS ALONG 
THE SOUTHERN EDGE OF THE GUIDANCE SUITE DUE TO THE STRONG EASTERLY 
SHEAR DISPLACING THE DEEP CONVECTION MORE TO THE WEST SIDE OF THE 
CIRCULATION.  THE STRONG LOW TO MID-LEVEL SUBTROPICAL RIDGE TO THE 
NORTH SHOULD ALSO PREVENT DALILA FROM GAINING MUCH LATITUDE.  THE 
CLIPER...AVN...AND UKMET MODELS WERE CLOSELY FOLLOWED.
 
THE GLOBAL MODELS AS WELL AS THE SHIPS INTENSITY MODEL HAVE NOT 
HANDLED THE UPPER-LEVEL SHEAR VERY WELL.  SATELLITE-DERIVED WINDS 
INDICATE A FAIRLY LONG EASTERLY FETCH OF 20 TO 30 KT WINDS COMING 
ACROSS CENTRAL MEXICO...SO IT IS DOUBTFUL THAT THERE WILL BE MUCH... 
IF ANY...DECREASE IN THE VERTICAL SHEAR BEFORE DALILA REACHES COOLER 
SSTS IN ABOUT 24 HOURS.  THEREFORE...STEADY WEAKENING IS FORECAST 
AFTER 24 HOURS...WHICH IS CONSISTENT WITH THE SHIPS AND GFDL MODELS.
 
THERE IS NO CHANGE IN THE WIND RADII FORECASTS BASED ON A 25/00Z 
UPPER-AIR OBSERVATION FROM SOCORRO ISLAND...WMO 76723...WHICH 
INDICATED 40 TO 45 KT WINDS FROM 1000 THROUGH 12000 FT IN THE 
NON-CONVECTIVE NORTHWEST QUADRANT.  THAT QUADRANT HAS SINCE FILLED 
IN WITH CONVECTION...SO THOSE STRONGER WINDS ARE LIKELY MAKING IT 
DOWN TO THE SURFACE NOW.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     25/0300Z 18.8N 111.1W    60 KTS
12HR VT     25/1200Z 19.2N 112.4W    60 KTS
24HR VT     26/0000Z 19.6N 114.0W    50 KTS
36HR VT     26/1200Z 20.0N 115.5W    40 KTS
48HR VT     27/0000Z 20.3N 116.9W    35 KTS
72HR VT     28/0000Z 20.5N 119.0W    30 KTS
 
 
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