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Tropical Storm MIRIAM Forecast Discussion Number 3

Issued at 800 AM PDT SAT SEP 22 2012

000
WTPZ43 KNHC 221435
TCDEP3
 
TROPICAL STORM MIRIAM DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
800 AM PDT SAT SEP 22 2012
 
THE CLOUD PATTERN ASSOCIATED WITH THE CYCLONE CONTINUES TO BECOME
BETTER ORGANIZED...WITH AN AREA OF COLD TOPS NEAR THE CENTER AND A
LARGE CONVECTIVE BAND TO THE SOUTHWEST. SATELLITE INTENSITY
ESTIMATES FROM TAFB...SAB...AND UW-CIMSS ALL SUPPORT NAMING THE
SYSTEM AT THIS TIME...AND THE INITIAL INTENSITY IS SET TO 35 KT.
MIRIAM IS IN A LOW-SHEAR ENVIRONMENT OVER VERY WARM WATERS...SO
STEADY STRENGTHENING IS LIKELY DURING THE NEXT COUPLE OF DAYS.
WHILE THERE ARE NO SIGNS OF AN INNER-CORE STRUCTURE THAT WOULD
SUGGEST RAPID INTENSIFICATION IS IMMINENT...THAT IS POSSIBLE DURING
THE NEXT DAY OR TWO IF AN INNER CORE CAN BECOME ESTABLISHED. THE
NEW NHC INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE THROUGH
THE FIRST COUPLE OF DAYS...SHOWING MIRIAM BECOMING A HURRICANE BY
36 HOURS IN AGREEMENT WITH THE SHIPS MODEL AND THE INTENSITY
CONSENSUS. LATE IN THE PERIOD...GRADUAL WEAKENING SHOULD OCCUR AS
THE CYCLONE MOVES OVER COOLER WATERS AND SOUTHWESTERLY SHEAR
INCREASES. THE NEW NHC FORECAST SHOWS SLOWER WEAKENING BY DAY 5 AS
MIRIAM SHOULD JUST BE NEARING THE 26C ISOTHERM AT THAT TIME.
 
THE CYCLONE APPEARS TO HAVE SLOWED DOWN OVER THE PAST FEW HOURS
WHILE IT ORGANIZES...AND THE INITIAL MOTION ESTIMATE IS A SOMEWHAT
UNCERTAIN 285/04. THE TRACK FORECAST REASONING REMAINS UNCHANGED...
AS MIRIAM WILL MOVE WEST-NORTHWESTWARD FOR THE NEXT COUPLE OF DAYS
ON THE SOUTHWESTERN FLANK OF A SUBTROPICAL RIDGE CENTERED OVER
NORTHERN MEXICO. THROUGH 48 HOURS THE GUIDANCE HAS TRENDED A LITTLE
TO THE NORTH WITH A FASTER FORWARD SPEED...AND THE NHC TRACK HAS
BEEN ADJUSTED IN THAT DIRECTION AND IS A LITTLE SOUTH OF THE TVCE
CONSENSUS. AT DAYS 3 THROUGH 5 A MID-LATITUDE TROUGH MOVING INTO
THE WESTERN UNITED STATES WILL WEAKEN THE RIDGE AND INDUCE A MORE
POLEWARD MOTION. THERE REMAINS SOME SPREAD IN THE GUIDANCE BY THE
END OF THE PERIOD...WITH THE GFDL AND HWRF SHOWING A NORTHWARD
MOTION...WHILE THE ECMWF AND UKMET TURN MIRIAM WESTWARD. LATE IN THE
PERIOD THE NHC TRACK SHOWS A SLOW NORTHWESTWARD TO NORTH-
NORTHWESTWARD MOTION...CLOSE TO THE PREVIOUS FORECAST AND A LITTLE
TO THE RIGHT OF THE TVCE CONSENSUS.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/1500Z 13.9N 107.7W   35 KT  40 MPH
 12H  23/0000Z 14.4N 108.7W   45 KT  50 MPH
 24H  23/1200Z 15.4N 110.1W   55 KT  65 MPH
 36H  24/0000Z 16.5N 111.9W   65 KT  75 MPH
 48H  24/1200Z 17.5N 113.6W   75 KT  85 MPH
 72H  25/1200Z 19.0N 116.0W   75 KT  85 MPH
 96H  26/1200Z 20.0N 117.0W   65 KT  75 MPH
120H  27/1200Z 21.0N 117.5W   55 KT  65 MPH
 
$$
FORECASTER BRENNAN
 

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