Hurricane Danielle Update 4

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HURRICANE DANIELLE DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062010
500 PM AST WED AUG 25 2010

DANIELLE HAS DEVELOPED A CURVED BAND OF CONVECTION AROUND THE CENTER
WITH CLOUD TOPS TO -80C...AND A FAINT EYE-LIKE FEATURE HAS BEEN SEEN
IN VISIBLE IMAGERY.  HOWEVER...A RECENT AMSU OVERPASS SUGGESTS THIS
IS DISPLACED TO THE NORTHEAST OF THE LOW-LEVEL CENTER.  ANALYSES
FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW THAT DANIELLE IS
STILL AFFECTED BY 10-15 KT OF SOUTHWESTERLY VERTICAL WIND
SHEAR...AND SEVERAL ARC CLOUDS HAVE BEEN SEEN JUST OUTSIDE THE
CENTRAL CONVECTION IN THE SOUTHWESTERN QUADRANT.

THE HURRICANE HAS TURNED TO THE RIGHT DURING THE PAST SEVERAL
HOURS...LIKELY DUE TO INTERACTION WITH AN UPPER-LEVEL LOW/TROUGH TO
ITS NORTHWEST.  THE INITIAL MOTION IS NOW 315/15.  FOR THE NEXT
48-72 HR...DANIELLE SHOULD BE STEERED BY THE FLOW BETWEEN THIS LOW
AND A LOW/MID-LEVEL RIDGE TO THE NORTH AND NORTHEAST...WHICH
SHOULD ALLOW A CONTINUED NORTHWESTWARD MOTION WITH SOME DECREASE IN
FORWARD SPEED.  AFTER 72 HR...DANIELLE SHOULD TURN NORTHWARD INTO A
WEAKNESS BETWEEN THE ATLANTIC RIDGE AND A LOW/MID-LEVEL RIDGE OVER
THE EASTERN UNITED STATES.  THE SPREAD OF THE TRACK GUIDANCE DURING
THIS TIME HAS INCREASED SINCE THE LAST ADVISORY...AND THE
CONFIDENCE IN THE FORECAST TRACK HAS CORRESPONDINGLY DECREASED. 
THE NOGAPS... HWRF...GFDN...AND GFS ENSEMBLE MEANS FORECAST A
NORTHWESTWARD MOTION BY 120 HR AND ARE ON THE LEFT SIDE OF THE
GUIDANCE ENVELOPE.  THE ECMWF AND THE LBAR SHOW A QUICK RECURAVTURE
TO THE NORTHEAST AND ARE ON THE RIGHT SIDE OF THE ENVELOPE.  THE
OTHER DYNAMICAL AND CONSENSUS MODELS FORECAST A MEANDERING
NORTHWARD MOTION...AND THE 72-120 HR FORECAST TRACK FOLLOWS THIS
SCENARIO.  OVERALL...THE NEW FORECAST TRACK IS A LITTLE TO THE
RIGHT OF THE PREVIOUS TRACK THROUGH 48-72 HR AND A LITTLE TO THE
LEFT OF IT THEREAFTER.
 
DANIELLE SHOULD PASS TO THE EAST AND NORTH OF THE NEARBY UPPER-LEVEL
TROUGH IN 12-18 HR...WHICH IS EXPECTED TO LEAD TO A DECREASE IN
THE SHEAR.  THE DYNAMICAL MODELS ARE NOT IN GOOD AGREEMENT ON THE
STRENGTH OF THE UPPER-LEVEL WINDS NEAR DANIELLE DURING THE 24-72 HR
TIME FRAME...WITH THE UKMET SHOWING CONSISTENTLY STRONGER SHEAR
THAN THE OTHER GUIDANCE.  THE INTENSITY FORECAST WILL LEAN TOWARDS
THE LIGHTER-SHEAR SCENARIO AND CALL FOR A PEAK INTENSITY OF 95 KT
IN 72 HR.  THIS IS AGAIN BETWEEN THE MORE AGGRESSIVE GFDL/GFDN AND
THE LESS AGGRESSIVE SHIPS/LGEM.  AFTER 72 HR...THE DYNAMICAL
MODELS AGREE THAT AN UPPER-LEVEL TROUGH DEVELOPING WEST OF DANIELLE
SHOULD CAUSE SIGNIFICANT SOUTHWESTERLY SHEAR...AND THE INTENSITY
FORECAST FOR THIS TIME THUS CALLS FOR ARRESTED DEVELOPMENT FOLLOWED
BY WEAKENING.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/2100Z 21.2N  53.1W    75 KT
 12HR VT     26/0600Z 22.3N  54.5W    75 KT
 24HR VT     26/1800Z 23.5N  56.4W    80 KT
 36HR VT     27/0600Z 24.8N  58.3W    85 KT
 48HR VT     27/1800Z 26.1N  60.2W    90 KT
 72HR VT     28/1800Z 29.0N  62.5W    95 KT
 96HR VT     29/1800Z 32.0N  62.5W    95 KT
120HR VT     30/1800Z 35.0N  62.5W    85 KT
 
$$
FORECASTER BEVEN

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