000 WTPZ45 KNHC 031454 TCDEP5 TROPICAL STORM JOHN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102012 800 AM PDT MON SEP 03 2012 EARLY MORNING MICROWAVE AND VISIBLE SATELLITE IMAGES INDICATE THAT THE CENTER OF JOHN IS EXPOSED TO THE NORTHEAST OF THE MAIN CLUSTER OF CONVECTION DUE TO MODERATE TO STRONG NORTHEASTERLY SHEAR. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB ARE 30 AND 35 KT... RESPECTIVELY...AND OBJECTIVE CI-NUMBERS FROM UW/CIMMS ARE T2.5. BASED ON THESE SATELLITE ESTIMATES THE INITIAL WIND SPEED REMAINS 35 KT. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BECOME EVEN MORE HOSTILE DURING THE NEXT DAY OR SO...WITH JOHN MOVING OVER COOLER WATERS AND THE MODERATE TO STRONG NORTHEASTERLY SHEAR CONTINUING. AS A RESULT...A GRADUAL SPIN DOWN OF THE LARGE CIRCULATION IS FORECAST DURING THE NEXT COUPLE OF DAYS. JOHN IS EXPECTED TO WEAKEN TO TROPICAL DEPRESSION BY TUESDAY MORNING...AND SHOULD BECOME A REMNANT LOW IN ABOUT 48 HOURS. JOHN WAS LOCATED SLIGHTLY NORTHEAST OF THE PREVIOUS ESTIMATES...BUT THE OVERALL MOTION IS STILL NORTHWESTWARD OR 305 DEGREES AT 11 KT. THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON A NORTHWESTWARD TRACK DURING THE NEXT COUPLE OF DAYS AS JOHN MOVES AROUND THE SOUTHWESTERN PORTION OF A MID-LEVEL RIDGE OVER THE SOUTH-CENTRAL UNITED STATES. THE NEW NHC TRACK IS A LITTLE EAST OF THE PREVIOUS ADVISORY...DUE TO THE MORE NORTHEASTWARD INITIAL POSTION. THE LATTER PORTION OF THE TRACK SHOWS SOME REDUCTION IN FORWARD SPEED AND A TURN TOWARD THE WEST-NORTHWEST AS JOHN BECOMES A SHALLOW SYSTEM AND IS STEERED BY THE LOW-LEVEL FLOW. THAT PORTION OF THE TRACK IS ON THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE CLOSE TO THE ECMWF MODEL...WHICH WAS A VERY GOOD PERFORMER FOR THE WEAKENING PHASE OF ILEANA. SOME MOISTURE FROM JOHN WILL LIKELY SPREAD OVER PORTIONS OF THE BAJA PENINSULA DURING THE NEXT DAY OR TWO. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 20.5N 112.6W 35 KT 40 MPH 12H 04/0000Z 21.3N 113.9W 35 KT 40 MPH 24H 04/1200Z 22.7N 115.7W 30 KT 35 MPH 36H 05/0000Z 24.0N 117.5W 30 KT 35 MPH 48H 05/1200Z 25.0N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 06/1200Z 26.5N 121.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 07/1200Z 27.0N 122.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/1200Z...DISSIPATED $$ FORECASTER BROWN