Hurricane JOHN

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HURRICANE JOHN DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP112006
800 PM PDT WED AUG 30 2006
 
DURING THE LAST SEVERAL HOURS...THE SATELLITE SIGNATURE ASSOCIATED
WITH JOHN HAS DEGRADED SLIGHTLY.  THE EYE HAS ONCE AGAIN BECOME
OBSCURED AND THE OVERALL SHAPE OF THE CLOUD CANOPY HAS BECOME
SOMEWHAT ELONGATED.  THIS MAY BE DUE TO AN EYEWALL REPLACEMENT
CYCLE THAT HAS CAUSED A FLUCTUATION IN INTENSITY.  THE INITIAL
INTENSITY IS LOWERED SLIGHTLY TO 110 KT BASED ON THE TRENDS IN
SATELLITE APPEARANCE. STILL...JOHN REMAINS A DANGEROUS CATEGORY
THREE HURRICANE ON THE SAFFIR-SIMPSON SCALE.

THE INTENSITY FORECAST IS QUITE PROBLEMATIC...GIVEN THE CLOSE
PROXIMITY TO LAND AND THE CURRENT EYEWALL REPLACEMENT. 
ADDITIONALLY...SOUTHERLY SHEAR APPEARS TO BE INCREASING AS AN
UPPER-LEVEL ANTICYCLONE HAS FORMED EAST OF JOHN OVER SOUTHERN
MEXICO.  SINCE THE OFFICIAL FORECAST TRACK REMAINS OFFSHORE AND
OVER VERY WARM WATERS...ADDITIONAL STRENGTHENING IS FORECAST UNDER
THE ASSUMPTION THAT THE CURRENT EYEWALL REPLACEMENT CYCLE WILL
COMPLETE.  INDEED...THE POTENTIAL EXISTS FOR JOHN TO BE A CATEGORY
FOUR HURRICANE AS IT APPROACHES THE BAJA PENINSULA.  THEREAFTER...
JOHN WILL ENCOUNTER PROGRESSIVELY COOLER WATERS WEST OF BAJA...
RESULTING IN WEAKENING. 
 
JOHN HAS BEEN MOVING WEST-NORTHWEST OR 300/14...DURING THE LAST 6 TO
12 HOURS. THIS IS A LITTLE TO THE LEFT OF THE PREVIOUS TRACK. 
GLOBAL MODELS ARE IN FAIRLY GOOD AGREEMENT ON JOHN CONTINUING
WEST-NORTHWEST TO NORTHWESTWARD...EFFECTIVELY PARALLELING THE COAST
OF MEXICO...AS IT ROUNDS THE SOUTHWESTERN PERIPHERY OF A MIDDLE- TO
UPPER-LEVEL RIDGE OVER NORTHERN MEXICO.  IN FACT...THE GFDL HAS
SHIFTED A LITTLE LEFT...OR WEST...IN BETTER AGREEMENT WITH THE
OTHER DYNAMICAL MODELS...AND NO LONGER SHOWS LANDFALL ALONG THE
COAST OF MEXICO DURING THE FIRST 48 HOURS.  BEYOND 48 HOURS...THE
GLOBAL MODELS BEGIN TO DIVERGE BASED ON THEIR DIFFERING DEPICTIONS
OF AN UPPER TROUGH OFF THE WEST COAST OF THE UNITED STATES.  MOST
OF THE MODELS...SAVE THE GFDL...LIFT THIS TROUGH NORTHEASTWARD
ALLOWING A MID-LEVEL RIDGE TO BUILD NORTH OF JOHN...RESULTING IN
THE CYCLONE TURNING TOWARD THE WEST.  THE GFDL KEEPS THE TROUGH IN
PLACE ALLOWING JOHN TO CONTINUE NORTHWESTWARD INTO THE GULF OF
CALIFORNIA.  WHILE THIS SOLUTION CANNOT BE COMPLETELY
DISCREDITED...ALL OF THE REMAINING DYNAMICAL MODELS TURN THE
CYCLONE WESTWARD AND SO DOES THE OFFICIAL FORECAST.
UNFORTUNATELY...THIS TURN TOWARD THE WEST IS FORECAST TO OCCUR VERY
CLOSE TO THE SOUTHERN TIP OF THE BAJA PENINSULA.  THIS MEANS THAT
HURRICANE CONDITIONS ARE LIKELY...EVEN IF THE CYCLONE DOES NOT MAKE
LANDFALL ON THE PENINSULA. AS A RESULT...A HURRICANE WARNING IS NOW
NEEDED FOR SOUTHERN PORTIONS OF THE BAJA PENINSULA.  ACCORDINGLY...
THE GOVERNMENT OF MEXICO HAS MADE SEVERAL CHANGES TO THE WATCHES
AND WARNINGS. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      31/0300Z 18.1N 104.5W   110 KT
 12HR VT     31/1200Z 19.3N 105.9W   115 KT
 24HR VT     01/0000Z 21.3N 107.2W   115 KT
 36HR VT     01/1200Z 22.4N 108.6W   115 KT
 48HR VT     02/0000Z 23.0N 109.8W   110 KT
 72HR VT     03/0000Z 23.8N 112.3W   100 KT
 96HR VT     04/0000Z 24.0N 116.5W    75 KT
120HR VT     05/0000Z 24.0N 121.0W    55 KT
 
$$
FORECASTER RHOME/BEVEN
 
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