Hurricane JOHN

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HURRICANE JOHN DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP112006
200 AM PDT WED AUG 30 2006
 
RADAR FROM ACAPULCO MEXICO SHOWS A WELL-DEFINED EYE AND IT APPEARS
THAT JOHN HAS GONE THROUGH AN EYE-WALL REPLACEMENT CYCLE.  THIS MAY
EXPLAIN WHY THE SATELLITE APPEARANCE HAS NOT IMPROVED MUCH SINCE
YESTERDAY AFTERNOON...HOWEVER WITHIN THE PAST HOUR OR SO A WARM
SPOT HAS RE-APPEARED IN INFRARED SATELLITE IMAGERY.  DVORAK
SATELLITE ESTIMATES ARE 102 KT AND 90 KT FROM TAFB AND SAB
RESPECTIVELY AND THE INITIAL INTENSITY WILL REMAIN 100 KT FOR THIS
ADVISORY.  AN AIR FORCE HURRICANE HUNTER AIRCRAFT IS CURRENTLY
EN-ROUTE TO JOHN AND IT SHOULD SOON PROVIDE A MUCH MORE ACCURATE
MEASURE OF THE HURRICANE'S CURRENT STRENGTH.
 
JOHN HAS BEEN MOVING BETWEEN WEST-NORTHWEST AND NORTHWEST AND THE
ESTIMATED MOTION IS 300/10.  THE GLOBAL MODELS KEEP JOHN ON THIS
GENERAL HEADING FOR THE NEXT 36 HOURS AROUND THE SOUTHWESTERN
PERIPHERY OF A MID- TO UPPER-LEVEL RIDGE OVER NORTHERN MEXICO.  THE
GFS REMAINS ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE DUE TO ITS
WEAKER DEPICTION OF THE CYCLONE.  THE GFDL AND UKMET ARE ON THE
RIGHT SIDE OF THE GUIDANCE AND BOTH TRACK JOHN ACROSS SOUTHWESTERN
MEXICO IN 24-36 HOURS.  OUT OF RESPECT FOR THE GFDL AND UKMET THE
TRACK FORECAST IS AGAIN SHIFTED RIGHT OR CLOSER TO THE COAST OF
MEXICO.  EVEN THOUGH THE OFFICIAL FORECAST KEEPS THE CENTER JUST
OFFSHORE...ANY SMALL DEVIATION TO THE RIGHT WILL BRING THE CORE OF
THIS DANGEROUS HURRICANE OVER SOUTHWEST MEXICO. BEYOND THREE DAYS
THERE REMAINS SIGNIFICANT DIVERGENCE IN THE MODELS AND HIGHER
THAN NORMAL UNCERTAINTY IN THE TRACK FORECAST.  AS WITH THE
PREVIOUS ADVISORY...IT IS ASSUMED THERE WILL BE ENOUGH RIDGING
TO THE NORTH OF JOHN TO BEND THE TRACK MORE WESTWARD AT DAYS 4
AND 5.
 
WITH LOW SHEAR AND WARM SSTS THE INTENSITY GUIDANCE CONTINUES TO
INDICATE STRENGTHENING.  BECAUSE INTENSIFICATION HAS CEASED OVER
THE PAST 12 HOURS...PERSISTENCE HAS BECOME LESS OF A POSITIVE 
FACTOR IN THE SHIPS MODEL AND THEREFORE IT NOW KEEPS THE HURRICANE
JUST BELOW CATEGORY FOUR STRENGTH. HOWEVER...IT IS ASSUMED THAT
JOHN HAS JUST COMPLETED AN EYEWALL REPLACEMENT CYCLE AND
STRENGTHENING SHOULD RESUME.  THE OFFICIAL INTENSITY FORECAST WILL
CONTINUE TO PREDICT A CATEGORY FOUR WITHIN THE NEXT 24 HOURS...
VIRTUALLY UNCHANGED FROM THE PREVIOUS ADVISORY.
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/0900Z 15.6N 101.3W   100 KT
 12HR VT     30/1800Z 16.5N 102.4W   110 KT
 24HR VT     31/0600Z 18.0N 104.2W   120 KT
 36HR VT     31/1800Z 19.5N 106.0W   120 KT
 48HR VT     01/0600Z 20.9N 107.7W   115 KT
 72HR VT     02/0600Z 22.2N 110.7W   105 KT
 96HR VT     03/0600Z 22.8N 114.0W    90 KT
120HR VT     04/0600Z 23.0N 118.0W    75 KT
 
$$
FORECASTER BROWN/STEWART
 
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