Hurricane DANIELLE

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TROPICAL STORM DANIELLE DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT WED AUG 18 2004
 
DANIELLE SHOWS A SHEARED CLOUD PATTERN THIS EVENING...WITH THE LOW
LEVEL CENTER EXPOSED TO THE SOUTHWEST OF AN AREA OF PERSISTENT
CONVECTION.  THE INITIAL INTENSITY OF 40 KT IS BASED ON A QUIKSCAT
OVERPASS AT 18/2036Z WITH UNCONTAMINATED 40 KT WINDS...AND A
COMBINATION OF SATELLITE INTENSITY ESTIMATES.

DANIELLE HAS TURNED RIGHT DURING THE PAST 6 HR AND THE INITIAL
MOTION IS NOW 055/9...AND THAT MAY BE GENEROUS ON THE SPEED.  THE
STORM IS EMBEDDED IN A LOW/MID LEVEL SUBTROPICAL RIDGE...WITH A
MID/UPPER-LEVEL SHORTWAVE RIDGE PASSING TO THE NORTH OF THE STORM
AND A STRONG MID/UPPER-LEVEL LOW TO THE WEST NEAR 33N45W.  LARGE-
SCALE MODELS SUGGEST A LOW AND ASSOCIATED UPPER-LEVEL SHORTWAVE
TROUGH WILL PASS NORTH OF DANIELLE DURING THE NEXT 72 HR...FOLLOWED
BY A DEEP LAYER RIDGE BUILDING NEAR THE AZORES.  TRACK GUIDANCE
RESPONDS TO THIS WITH SOME DIVERGENCE.  THE GFS LOSES DANIELLE
QUICKLY...WHILE THE GFDL STALLS THE CYCLONE FOR 72 HR FOLLOWED BY A
NORTH-NORTHWESTWARD MOTION.  THE UKMET/NOGAPS CALL FOR A SLOW
NORTHEASTWARD MOTION FOR 72-96 HR...WITH THE NOGAPS TURNING
NORTHWESTWARD AFTER THAT.  THE OFFICIAL FORECAST FOLLOWS THE
UKMET/NOGAPS FOR 96 HR...BUT SHOWS LESS OF A TURN THAN THE NOGAPS
AT 120 HR.  THE NEW TRACK IS ABOUT A DEGREE SOUTH OF AND SLOWER
THAN THE PREVIOUS TRACK.
 
DANIELLE SHOULD STAY OVER 25-26C SEA SURFACE TEMPERATURES THROUGH 72
HR...SO THE BIGGEST INTENSITY QUESTION IS HOW MUCH SHEAR WILL OCCUR. 
THE MODELS AGAIN DIVERGE ON THE UPPER-LEVEL WIND PATTERN.  THE
GFS/CANADIAN MODELS TAKE THE UPPER-LEVEL LOW WEST OF DANIELLE AND
MOVE IT BODILY EASTWARD ACROSS THE CYCLONE...WHICH WOULD LIKELY
DESTROY DANIELLE.  THE UKMET/NOGAPS ALSO MOVE THE LOW EASTWARD BUT
WEAKENING IT RAPIDLY WHILE DOING SO...WHICH COULD LEAVE DANIELLE IN
A LOWER SHEAR ENVIRONMENT AND ALLOW IT TO MAINTAIN SOME STRENGTH. 
THE INTENSITY FORECAST COMPROMISES BETWEEN THESE TWO SOLUTIONS...
CALLING FOR A GRADUAL WEAKENING IN BEST AGREEMENT WITH THE GFDL. 
BY 72 HR...A COLD FRONT ASSOCIATED WITH THE LOW TO THE NORTH SHOULD
REACH DANIELLE AND CAUSE EXTRATROPICAL TRANSITION.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/0300Z 29.6N  37.5W    40 KT
 12HR VT     19/1200Z 30.2N  36.7W    35 KT
 24HR VT     20/0000Z 31.2N  35.8W    30 KT
 36HR VT     20/1200Z 32.3N  35.0W    25 KT
 48HR VT     21/0000Z 33.1N  33.9W    25 KT
 72HR VT     22/0000Z 34.5N  31.0W    25 KT...EXTRATROPICAL
 96HR VT     23/0000Z 36.0N  28.0W    25 KT...EXTRATROPICAL
120HR VT     24/0000Z 38.0N  27.0W    25 KT...EXTRATROPICAL
 
 
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