ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:43 UTC