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TROPICAL STORM DALILA DISCUSSION NUMBER 25
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT THU JUL 26 2001
DALILA CONTINUES TO GENERATE PULSES IN THE CDO PATTERN LIKE IT HAS
THE PAST 3 NIGHTS AS THE VERTICAL SHEAR WEAKENS AT NIGHT AND THEN
INCREASES AGAIN DURING THE DAY. THE INITIAL INTENSITY OF 55 KT IS
BASED ON DVORAK SATELLITE INTENSITY ESTIMATES OF 55 KT...T3.5...FROM
TAFB AND AFWA...AND 65 KT...T4.0 EMBEDDED CENTER...FROM SAB. THE
INTENSITY WAS HELD AT 55 KT SINCE EMBEDDED CENTER PATTERN HAS NOT
BEEN PERSISTING FOR MORE THAN A COUPLE HOURS BEFORE WEAKENING AGAIN.
THE INITIAL MOTION ESTIMATE IS 285/8 OVER THE PAST 12 HOURS. DURING
THE PAST 6 HOURS...THE MOTION HAS BEEN CLOSER TO 275 DEGREES. THE
INITIAL POSITION WAS KEPT SLIGHTLY NORTH OF THE SATELLITE FIX
POSITIONS TO SMOOTH OUT THE SHEAR-INDUCED WOBBLES IN THE TRACK.
THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK
PHILOSOPHY. THE LATEST MODEL GUIDANCE IS EVEN MORE TIGHTLY CLUSTERED
ABOUT A WEST-NORTHWESTWARD OR WESTWARD TRACK THROUGHOUT THE FORECAST
PERIOD. IN FACT...THE AVN MODEL IS NOW THE SOUTHERNMOST OF ALL THE
DYNAMICAL MODELS AND TAKES THE CYCLONE MORE WESTWARD. THE OFFICIAL
TRACK IS CLOSE TO THE UKMET-AVN CONSENSUS AND JUST A LITTLE SOUTH OF
THE PREVIOUS FORECAST TRACK.
THE AFOREMENTIOEND VERTICAL SHEAR ACROSS DALILA CONTINUES TO HAVE A
DISTINCT DIURNAL FLUCTUATION. ANOTHER SURGE IN THE EASTERLY
UPPER-LEVEL FLOW CAN BE SEEN IN SATELLITE IMAGERY PASSING SOCORRO
ISLAND. THAT SURGE SHOULD BE IMPINGING ON THE CYCLONE WITHIN THE
NEXT 12 HOURS OR LESS. AS SUCH...SLOW BUT STEADY WEAKENING IS
FORECAST SINCE DALILA WILL ALSO BE MOVING OVER SUB-25C SST WATER IN
6 TO 12 HOURS. THIS SCENARIO IS CONSISTENT WITH THE SHIPS INTENSITY
MODEL AND THE PREVIOUS FORECAST INTENSITY TREND.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 27/0300Z 20.2N 115.9W 55 KTS
12HR VT 27/1200Z 20.6N 117.1W 50 KTS
24HR VT 28/0000Z 21.0N 118.5W 45 KTS
36HR VT 28/1200Z 21.3N 120.0W 40 KTS
48HR VT 29/0000Z 21.4N 121.2W 30 KTS
72HR VT 30/0000Z 21.5N 123.5W 25 KTS...DISSIPATING
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