Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED SEP 10 2003
 
SATELLITE IMAGERY INDICATES ANOTHER STRONG CONVECTIVE BURST HAS
DEVELOPED IN THE NORTHERN EYEWALL. THIS HAS SENT CIRRUS CLOUDS
SPREADING SOUTHWARD AND OBSCURING THE NORTHERN HALF OF THE LARGE
EYE. THEREFORE...THE INITIAL POSITION IS JUST A TAD NORTH OF THE
SATELLITE POSITIONS. ISABEL REMAINS A POWERFUL HURRICANE BASED ON A
SATELLITE INTENSITY ESTIMATE OF 115 KT FROM ALL THREE AGENCIES.
OUTFLOW ALSO REMAINS VERY IMPRESSIVE AND HAS IMPROVED TO THE WEST
AND TO THE EAST...WHILE BECOMING SLIGHTLY RESTRICTED TO THE NORTH.

THE INITIAL MOTION ESTIMATE IS 280/10. THERE MAY BE SOME WOBBLE IN
THE TRACK OVER THE PAST 6 HOUR... WHICH IS FAIRLY TYPICAL OF
INTENSE HURRICANES. RECENT SATELLITE FIX POSITIONS SUGGEST A SHARP
DUE WEST MOTION OF 270 DEGREES. HOWEVER...I WOULD PREFER TO WAIT
UNTIL THE EYE BECOMES MORE DISTINCT BEFORE TAKING ISABEL OFF ON A
DUE WESTWARD TRACK. OTHER THAN THAT...THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. THE 06Z GFS AND
NOGAPS MODELS HAVE FINALLY ABANDONED THEIR SLIGHT SOUTHWARD JOG AND
ACTUALLY LOOK QUITE REASONABLE. THE GFDL AND UKMET MODELS...HOWEVER
...HAVE MORE POLEWARD MOTION...AND THE UKMET NOW APPEARS TO HAVE
DEVELOPED A RIGHT-OF-TRACK BIAS. THEREFORE...THE GFS AND NOGAPS
SOLUTIONS WERE FOLLOWED FOR THIS ADVISORY...WHICH SEEMS CONSISTENT
WITH THE CURRENT 5-WAVE MID-LATITUDE LONGWAVE PATTERN OVER THE
NORTHERN HEMISPHERE. THE STRONGEST ANCHOR LOW/TROUGH IS LOCATED
OVER SOUTHERN GREENLAND AND EXTENDS SOUTHWARD ALONG 45W LONGITUDE.
MAINTAINING A 5-WAVE PATTERN SPACING WOULD EVENTUALLY YIELD A
LONGWAVE TROUGH OVER THE CENTRAL U.S. IN 3-5 DAYS...WITH A RIDGE
ALONG AND EAST OF THE U.S. EAST COAST...AS DEPICTED BY THE GFS.

THE OUTFLOW ON THE WEST SIDE OF ISABEL IS EXPANDING WESTWARD AND IS
STARTING TO GET DRAWN INTO THE LARGE MID-/UPPER-LOW NORTH OF PUERTO
RICO. OUTFLOW TO THE EAST IS ALSO EXPANDING...SO SOME ADDITIONAL
STRENGTHENING IS POSSIBLE AT ANY TIME. HOWEVER...TIMING THE EFFECTS
OF INNER-CORE CONVECTIVE CHANGES IS IMPOSSIBLE MORE THAN ABOUT 12
HOURS IN ADVANCE...SO THE INTENSITY FORECAST SHOWS LITTLE CHANGE.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/1500Z 21.3N  50.9W   115 KT
 12HR VT     11/0000Z 21.5N  52.4W   115 KT
 24HR VT     11/1200Z 21.7N  54.4W   115 KT
 36HR VT     12/0000Z 21.8N  56.0W   115 KT
 48HR VT     12/1200Z 21.9N  57.8W   115 KT
 72HR VT     13/1200Z 22.0N  61.0W   115 KT
 96HR VT     14/1200Z 23.0N  64.5W   110 KT
120HR VT     15/1200Z 23.5N  68.0W   110 KT
 
 
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