Tropical Storm JUAN

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TROPICAL STORM JUAN DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT FRI SEP 26 2003
 
AFTER COMING OUT OF THE GOES-12 SATELLITE ECLIPSE PERIOD...NEW
IMAGERY INDICATES THAT JUAN HAS BECOME BETTER ORGANIZED AND HAS
ALSO STARTED MOVING NORTHWARD AGAIN. AN EYE-LIKE FEATURE WAS
APPARENT IN THE MID-CLOUDS OF THE PRE-ECLIPSE IMAGERY...BUT NO DEEP
CONVECTION WAS WITHIN 100 NMI OF THE CENTER. HOWEVER...THE EYE
FEATURE IS NOW OBSCURED BY DEEP CONVECTION...TOPS COLDER THAN
-70C...THAT HAVE SURROUNDED MORE THAN 50 PERCENT OF THE INNER CORE
CIRCULATION. ALTHOUGH SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS
T2.5...OR 35 KT...I HAVE OPTED TO INCREASE THE INTENSITY SLIGHTLY
BASED ON THIS NEW INNER-CORE CONVECTIVE BANDING AND RECENT AMSU
INTENSITY ESTIMATES OF 990-992 MB.
 
THE INITIAL MOTION ESTIMATE IS 350/08. THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS TRACK OR INTENSITY FORECAST. THE NHC MODEL
GUIDANCE SHOWS GOOD CONVERGENCE ABOUT THE PREVIOUS FORECAST TRACK
AND IS ALSO IN GOOD AGREEMENT ON TAKING JUAN NORTH TO
NORTH-NORTHWESTWARD AND GRADUALLY ACCELERATE THE CYCLONE THROUGH 72
HOURS AS A SERIES OF NEGATIVELY TILTED SHORTWAVE TROUGHS UNDERCUT
THE SYSTEM FROM THE WEST AND SOUTH. BY 96 HOURS OR SO...JUAN IS
EXPECTED TO BE OVER THE CANADIAN MARITIMES REGION AND STARTING TO
BECOME EXTRATROPICAL AS THE CYCLONE BEGINS TO INTERACT WITH AND
EVENTUALLY BECOME ABSORBED BY A LARGER EXTRATROPICAL LOW PRESSURE
SYSTEM. THERE IS A LARGE SPREAD IN THE MODEL GUIDANCE BY 96 HOURS
WITH NOGAPS TAKING JUAN THE FARTHEST TO THE NORTHEAST OVER NORTHERN
NEWFOUNDLAND...WHILE THE REST OF THE NHC MODEL GUIDANCE TAKES THE
CYCLONE OVER THE ENTIRE LENGTH OF NOVA SCOTIA. THE OFFICIAL
FORECAST TRACK IS ONLY SLIGHTLY TO THE LEFT OF THE PREVIOUS
TRACK...AND IS CLOSE TO THE GFS AND GFDL MODELS.
 
IT WOULD NOT TAKE MUCH CONVECTION TO WRAP ALL THE AROUND THE
INNER-CORE OF JUAN AND PRODUCE AN EYE. WITH THIS IN MIND...THE
INTENSITY WAS INCREASED SLIGHTLY...BUT NIT AS HIGH AS THE SHIPS AND
GFDL INTENSITY MODELS WHICH BRING JUAN UP TO 75 KT AND 83 KT...
RESPECTIVELY...IN 36 HOURS. UPPER-LEVEL SHEAR WILL GRADUALLY
INCREASE TO MORE THAN 20 KT BY 24 HOURS...AND THIS IS THE PRIMARY
REASON FOR REMAINING BELOW THE MODEL GUIDANCE AT THIS TIME.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0900Z 31.5N  61.9W    55 KT
 12HR VT     26/1800Z 32.5N  62.2W    60 KT
 24HR VT     27/0600Z 34.3N  62.6W    65 KT
 36HR VT     27/1800Z 36.3N  63.3W    65 KT
 48HR VT     28/0600Z 38.4N  63.8W    60 KT
 72HR VT     29/0600Z 46.0N  63.0W    55 KT...EXTRATROPICAL INLAND
 96HR VT     30/0600Z 50.5N  60.5W    50 KT...EXTRATROPICAL INLAND
120HR VT     01/0600Z...ABSORBED BY LARGER EXTRATROPICAL LOW
 
 
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