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 516 
 WTPZ41 KNHC 310245
 TCDEP1
 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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