Tropical Storm JOHN

ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
 
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
 
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