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HURRICANE DANIELLE DISCUSSION NUMBER  20
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SAT AUG 29 1998
 
THE AIR FORCE RECONN MISSION WHICH COVERED THE 00Z AND 06Z FIXES
REPORTED FLIGHT LEVEL WINDS IN THE MID SEVENTIES OVER THE NORTHERN
QUADRANTS.  CENTRAL PRESSURES RANGED FROM 989 TO 991 MB.  DVORAK
SATELLITE ESTIMATES REMAIN BETWEEN 77 AND 90 KNOTS.
 
THEREFORE DANIELLE INITIAL INTENSITY WILL REMAIN AT 80 KNOTS.  THE
VERTICAL SHEAR CONTINUES TO BE FORECAST TO RELAX AND EVEN NOW THE
ENVIRONMENT SEEMS FAVORABLE FOR SOME STRENGTHENING BUT IT HAS YET TO
MATERIALIZE.  IN KEEPING WITH THE SHIPS FORECAST INTENSITY MODEL...
THE FORECAST INTENSITY WILL BE KEPT AT 80 KNOTS THROUGH 12 HOURS AND
THEN INCREASE AT A MODEST RATE.
 
DANIELLE INITIAL MOTION IS 300/12...A LITTLE MORE NORTHERLY THAN
PREVIOUSLY BECAUSE OF A MORE SOUTHERLY INITIAL POSITION.  THE RIDGE
NORTH OF DANIELLE IS EXPECTED TO WEAKEN IN 48 HOURS OVER THE WESTERN
ATLANTIC WHILE A STRONG MID-LATITUDE TROUGH IS FORECAST TO MOVE OVER
THE EASTERN UNITED STATES IN THAT SAME TIME FRAME.  IN RESPONSE TO
THAT PATTERN...ALL TRACK MODELS REMAIN IN GOOD AGREEMENT AND
CONSISTENTLY TURN DANIELLE NORTHWARD AND NORTHEASTWARD AHEAD OF THE
TROUGH BEYOND 48 HOURS.
 
THE QUESTION OF DANIELLE SLOWING DOWN AFTER THE 36 HOUR FORECAST
PERIOD REMAINS WITH THE 00Z AVIATION RUN.  NOGAPS AND THE UKMET
MODELS FOR 00Z DO NOT SLOW DANIELLE AND INDEED ACCELERATE IT TO THE
NORTHEAST AFTER THE TURN AT 48 HOURS.  SINCE THE AVIATION RUN
APPEARS TO HAVE A GOOD HANDLE ON THE APPROACHING SHORT WAVE TROUGH,
IT IS THOUGHT THAT THE SPURIOUS VORTEX TO THE EAST MUST BE
DISRUPTING THE RIDGE.
 
ANALYSIS OF THE JET DROPS SHOW A GOOD RIDGE THROUGH 400 MB NORTH OF
DANIELLE.  THE DROPS DO NOT EXTEND FAR ENOUGH EAST TO PREVENT THE
SPURIOUS VORTEX FROM GENERATING.
 
GROSS
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     29/0900Z 24.6N  68.9W    80 KTS
12HR VT     29/1800Z 25.4N  70.6W    80 KTS
24HR VT     30/0600Z 26.6N  72.3W    85 KTS
36HR VT     30/1800Z 28.3N  73.6W    90 KTS
48HR VT     31/0600Z 31.0N  73.7W    95 KTS
72HR VT     01/0600Z 34.0N  71.0W   100 KTS
 
 
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