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