ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM HURRICANE JOHN DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP112006 800 PM PDT TUE AUG 29 2006 JOHN'S EARLIER RAPID INTENSIFICATION APPEARS TO HAVE ABATED FOR NOW. THE EYE HAS BECOME INCREASINGLY OBSCURED DURING THE LAST FEW HOURS...WITH ONLY A RELATIVE WARM SPOT VISIBLE IN RECENT INFRARED IMAGERY. SUBJECTIVE SATELLITE INTENSITY ESTIMATES ARE 90 KT FROM BOTH TAFB AND SAB. GIVEN THE RESTRICTIONS OF THE DVORAK TECHNIQUE AND RAW DATA T-NUMBERS THAT REMAIN NEAR 115 KT...THE INITIAL INTENSITY IS HELD AT 100 KT. INNER CORE STRUCTURAL CHANGES MAY BE RESPONSIBLE FOR THE DEGRADATION OF THE SATELLITE APPEARANCE AND THERE ARE NO OBVIOUS ENVIRONMENTAL FACTORS TO PREVENT FURTHER STRENGTHENING. THE GFDL MODEL FORECASTS JOHN TO MOVE INLAND OVER MEXICO RESULTING IN RAPID WEAKENING AFTER 24 HOURS...HOWEVER SINCE THE OFFICIAL TRACK FORECAST KEEPS THE CYCLONE OVER WATER JOHN IS FORECAST TO BECOME A CATEGORY 4 HURRICANE IN 24 HOURS. JOHN HAS BEEN MOVING MORE TOWARD THE NORTHWEST NEAR 300/10 DURING THE LAST 6 TO 12 HOURS...AND THIS MOTION IS A LITTLE TO THE RIGHT OF THE PREVIOUS TRACK. MOST OF THE GLOBAL MODELS SHOW JOHN CONTINUING ON A GENERAL WEST-NORTHWEST TO NORTHWEST MOTION DURING THE NEXT 48 HOURS AS THE CYCLONE ROUNDS THE SOUTHWESTERN PERIPHERY OF A MIDDLE TO UPPER-LEVEL RIDGE OVER NORTHERN MEXICO. THE GFS CONTINUES TO HAVE A WEAKER REPRESENTATION OF THE CYCLONE... RESULTING IN A MORE WESTWARD TRACK. CONVERSELY...THE GFDL CONTINUES TO LIE ALONG THE FAR RIGHT SIDE OF THE MODEL SUITE...TAKING JOHN INLAND OVER MEXICO IN THE NEXT 24 HOURS. GIVEN THE MORE NORTHWARD INITIAL MOTION...THE EASTWARD TREND IN THE GLOBAL MODEL GUIDANCE... AND THE PERSISTENCE OF THE GFDL...THE OFFICIAL FORECAST IS SHIFTED CLOSER TO THE MEXICAN COAST FOR THE FIRST 72 HOURS. THIS REQUIRES THE ISSUANCE OF HURRICANE WATCHES AND WARNINGS AT THIS TIME. BEYOND 72 HOURS...SIGNIFICANT DIVERGENCE EXISTS IN THE MODEL GUIDANCE. THE GFS...NOGAPS...AND UKMET SHOW A MIDDLE- TO UPPER-LEVEL RIDGE BUILDING WESTWARD FROM NORTHERN MEXICO... RESULTING IN A SHARP TURN TOWARD THE WEST. THE ECMWF AND THE GFDL SHOW LITTLE OR NO RIDGING NORTH OF THE CYCLONE...ALLOWING A CONTINUATION OF THE NORTHWESTWARD TRACK. THE OFFICIAL FORECAST IS NUDGED NORTHWARD AT DAYS 4 AND 5 IN CONSIDERATION OF THE GFDL AND ECMWF BUT STILL SHOWS A TURN TOWARD THE WEST. IT SHOULD NOTED THAT THERE IS GREATER THAN USUAL UNCERTAINTY IN THE TRACK FORECAST AT THE LATER PERIODS...DUE TO THE MODEL SPREAD AND POSSIBLE INTERACTION WITH A TROPICAL DISTURBANCE LOCATED FARTHER WEST. FORECAST POSITIONS AND MAX WINDS INITIAL 30/0300Z 15.2N 100.4W 100 KT 12HR VT 30/1200Z 16.0N 101.7W 115 KT 24HR VT 31/0000Z 17.2N 103.7W 120 KT 36HR VT 31/1200Z 18.8N 105.7W 120 KT 48HR VT 01/0000Z 20.2N 107.6W 115 KT 72HR VT 02/0000Z 21.8N 111.0W 110 KT 96HR VT 03/0000Z 22.5N 114.5W 100 KT 120HR VT 04/0000Z 22.5N 118.0W 90 KT $$ FORECASTER RHOME/FRANKLIN NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:43 UTC