ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM JOHN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102012 200 PM PDT MON SEP 03 2012 SATELLITE IMAGERY SHOWS THAT THE ORGANIZATION OF JOHN IS GRADUALLY DECLINING WITH THE CENTER EXPOSED WELL TO THE NORTH OF THE REMAINING CONVECTIVE BAND. RECENT ASCAT DATA WERE NOT HELPFUL FOR DETERMINING THE CURRENT INTENSITY AS THE OVERPASS ONLY SAMPLED THE WESTERN PORTION OF THE CIRCULATION. A SHIP OBSERVATION OF 28 KT OVER THE FAR NORTHEASTERN PORTION OF THE LARGE CIRCULATION SUGGESTS THAT 30 TO 35 KT WINDS ARE LIKELY STILL OCCURRING NEARER TO THE CENTER. BASED ON THE SHIP OBSERVATION AND A DVORAK CI-NUMBER OF T2.5 FROM SAB...THE INITIAL WIND SPEED IS HELD AT 35 KT. THE NORTHEASTERLY SHEAR AFFECTING JOHN IS EXPECTED TO CONTINUE AS THE CYCLONE MOVES OVER PROGRESSIVELY COOLER WATERS DURING THE FORECAST PERIOD. THESE FACTORS SHOULD CAUSE GRADUAL WEAKENING AND JOHN IS FORECAST TO BECOME A TROPICAL DEPRESSION WITHIN 12 HOURS...AND A REMNANT LOW WITHIN A COUPLE OF DAYS. JOHN HAS BEEN MOVING NORTHWESTWARD OR 305 DEGREES AT 12 KT. THE CYCLONE SHOULD CONTINUE HEADING NORTHWESTWARD AROUND THE SOUTHWESTERN PORTION OF A MID-LEVEL RIDGE OVER THE SOUTH-CENTRAL UNITED STATES. THE MODELS ARE IN GOOD AGREEMENT ON THIS SCENARIO AND THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...AND NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. SOME MOISTURE FROM JOHN WILL LIKELY SPREAD OVER THE SOUTHERN PORTIONS OF THE BAJA PENINSULA DURING THE NEXT DAY OR TWO. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 21.1N 114.0W 35 KT 40 MPH 12H 04/0600Z 22.1N 115.6W 30 KT 35 MPH 24H 04/1800Z 23.4N 117.4W 30 KT 35 MPH 36H 05/0600Z 24.6N 119.0W 25 KT 30 MPH 48H 05/1800Z 25.6N 120.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 06/1800Z 27.0N 122.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 07/1800Z 27.5N 122.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/1800Z...DISSIPATED $$ FORECASTER BROWN NNNN
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Page last modified: Monday, 31-Dec-2012 12:10:29 UTC