Tropical Storm JUAN

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TROPICAL STORM JUAN DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU SEP 25 2003
 
WATER VAPOR IMAGERY SUGGESTS THAT JUAN MAY NOT BE FULLY TROPICAL...
AS THE STORM IS TANGLED WITH AN UPPER-LEVEL LOW TO THE SOUTHEAST. 
CONVECTION HAS DECREASED OVER THE PAST 6 HR...WHICH IS NOT UNUSUAL
FOR A QUASI-TROPICAL SYSTEM AT THIS STAGE OF DEVELOPMENT.  THE BEST
EVIDENCE OF THE TROPICAL NATURE OF JUAN IS REPORTS FROM DRIFTING
BUOY 41537...WHICH INCLUDED A PRESSURE OF 992.6 MB AT 20Z.  THIS
INDICATES THAT JUAN HAS THE TIGHT INNER CORE OF A TROPICAL CYCLONE. 
RIGHT NOW...JUAN IS SIMILAR TO KAREN IN 2001...ALTHOUGH IT IS NOT
AS STRONG OR AS BAROCLINIC IN ORIGIN AS KAREN WAS.  BASED ON THE
BUOY DATA AND THE PREVIOUS ADVISORY...THE MAXIMUM WINDS ARE
INCREASED TO 50 KT.

THE INITIAL MOTION HAS SLOWED TO 345/5...AND EVEN THAT MAY BE A
LITTLE TOO FAST.  WATER VAPOR IMAGERY SHOWS THAT JUAN IS ON THE
SOUTHWEST SIDE OF A BLOCKING MID/UPPER-LEVEL RIDGE OVER THE WEST
CENTRAL ATLANTIC...AND BETWEEN DEEP TROUGHS OVER THE EASTERN UNITED
STATES AND THE EASTERN ATLANTIC.  THE TROUGHING OVER THE EASTERN
UNITED STATES IS FORECAST TO ERODE THE RIDGE ENOUGH FOR JUAN TO
MOVE GENERALLY NORTH-NORTHWESTWARD FOR 48-72 HR...FOLLOWED BY
RECURVATURE TO THE NORTH AND NORTHEAST.  ALL GUIDANCE EXCEPT THE
UKMET AGREES WITH THIS SCENARIO.  THE OFFICIAL FORECAST WILL AS
WELL...WITH THE FORECAST BEING SLIGHTLY SLOWER AND A LITTLE TO THE
LEFT OF THE PREVIOUS TRACK.  IT SHOULD BE NOTED THAT THE UKMET IS A
MAJOR OUTLIER...CALLING FOR A SLOW EASTWARD DRIFT FOR THE NEXT
THREE DAYS.

THE INTENSITY FORECAST IS SOMEWHAT PROBLEMATIC.  JUAN IS EMBEDDED IN
UPPER-LEVEL WESTERLY TO SOUTHWESTERLY FLOW...AND LARGE-SCALE MODELS
FORECAST THE CYCLONE TO BE AFFECTED BY ONE OR MORE SHORTWAVE
TROUGHS DURING THE NEXT 72 HR.  THESE WILL LIKELY CAUSE SHEAR...AS
FORECAST BY THE SHIPS MODEL.  HOWEVER...THEY COULD ALSO CAUSE
DYNAMICAL FORCING OR UPPER-LEVEL DIVERGENCE THAT COULD SUSTAIN THE
CYCLONE. THE INTENSITY FORECAST WILL CALL FOR SLOW STRENGTHENING
FOR 24-36 HR.  HOWEVER...THE CURRENTLY FORECAST SHEAR SHOULD MAKE
IT DIFFICULT FOR ONE TO STRENGTHEN INTO A HURRICANE...ANMD THE
FORECAST WILL NOT CALL FOR THAT AT THIS TIME.  JUAN SHOULD LOSE
TROPICAL CHARACTERISTICS AFTER 72 HR AND BE ABSORBED BY A LARGE LOW
ASSOCIATED WITH THE EASTERN U.S. TROUGH BY 120 HR.

FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0300Z 31.1N  61.9W    50 KT
 12HR VT     26/1200Z 32.1N  62.2W    55 KT
 24HR VT     27/0000Z 33.7N  62.5W    60 KT
 36HR VT     27/1200Z 35.6N  63.1W    60 KT
 48HR VT     28/0000Z 37.6N  63.5W    60 KT
 72HR VT     29/0000Z 42.5N  64.0W    60 KT
 96HR VT     30/0000Z 49.0N  61.0W    50 KT...EXTRATROPICAL
120HR VT     01/0000Z...ABSORBED BY LARGER EXTRATROPICAL LOW
 
 
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