000 WTPZ43 KNHC 251452 TCDEP3 HURRICANE MIRIAM DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132012 800 AM PDT TUE SEP 25 2012 THE OVERALL SATELLITE APPEARANCE OF MIRIAM HAS NOT CHANGED MUCH DURING THE LAST 6 HOURS. THE CLOUD PATTERN REMAINS WELL ORGANIZED...CONSISTING OF A CIRCULAR CENTRAL DENSE OVERCAST COMPRISED OF PLENTY OF OF DEEP CONVECTION. SATELLITE DATA SUGGEST THAT AN EYEWALL REPLACEMENT CYCLE IS STILL ONGOING...WITH A FRAGMENT OF THE INNER EYEWALL LIKELY REMAINING AND AN OUTER EYEWALL AT ABOUT 30 N MI RADIUS GRADUALLY CONTRACTING. DVORAK T- AND CI-NUMBERS ARE 4.5 FROM TAFB AND SAB...BUT UW-CIMSS ADT CI VALUES ARE AT 5.6. THE INITIAL INTENSITY IS LOWERED TO 85 KT...BASED ON A BLEND OF THE ABOVE DATA. THE FORWARD SPEED OF MIRIAM HAS BEEN SLOWING DURING THE LAST 12-24 HOURS. A LONGER-TERM AVERAGE OF CENTER FIXES GIVES AN INITIAL MOTION ESTIMATE OF 300/04. MIRIAM SHOULD TURN NORTH-NORTHWESTWARD SOON AS IT MOVES AROUND THE WESTERN SIDE OF A MID-LEVEL RIDGE CENTERED OVER THE GULF OF MEXICO. A SLOW NORTHWARD MOTION IS EXPECTED BY 36 HOURS AS THE CYCLONE MOVES INTO A WEAKNESS ALONG 115W. A MID- TO UPPER-LEVEL CLOSED LOW FORMING OFFSHORE OF THE SOUTHERN CALIFORNIA COAST IN 2-3 DAYS COULD ALLOW FOR A NORTH- NORTHEAST MOTION BY DAY 3. THE NHC TRACK FORECAST IS VIRTUALLY UNCHANGED FROM THE PREVIOUS ONE...CLOSE TO THE MULTI-MODEL CONSENSUS TVCE THROUGH 36 HOURS AND IN BETWEEN THE ECMWF AND GFS AT LATER TIMES. THE EYEWALL REPLACEMENT CYCLE WILL NOT LIKELY COMPLETE ITSELF BEFORE MIRIAM MOVES OVER MARGINAL SSTS AND INTO AN ENVIRONMENT OF INCREASING WESTERLY SHEAR IN ABOUT 12-24 HOURS. DURING THE NEXT COUPLE OF DAYS...A PREVAILING MODERATE TO STRONG SOUTHWESTERLY SHEAR AND SLOWLY DECREASING SSTS SHOULD RESULT IN A STEADY WEAKENING OF THE CYCLONE. A FURTHER INCREASE IN SOUTHWESTERLY SHEAR ASSOCIATED WITH THE AFOREMENTIONED CLOSED LOW TO THE NORTHWEST OF MIRIAM SHOULD OCCUR AFTER 72 HOURS. RAPID WEAKENING IS FORECAST AFTER THAT TIME AND MIRIAM COULD DECOUPLE ENTIRELY...AS DEPICTED IN BOTH THE GFS/ECMWF MODEL SOLUTIONS. THE NHC INTENSITY FORECAST IS LOWER COMPARED TO THE PREVIOUS ONE...BUT NOT AS LOW AS THE SHIPS... LGEM AND FSSE OUTPUT SUGGESTS. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 18.7N 114.5W 85 KT 100 MPH 12H 26/0000Z 19.3N 114.7W 80 KT 90 MPH 24H 26/1200Z 20.2N 115.0W 70 KT 80 MPH 36H 27/0000Z 21.2N 115.2W 60 KT 70 MPH 48H 27/1200Z 22.2N 115.4W 50 KT 60 MPH 72H 28/1200Z 23.9N 115.3W 40 KT 45 MPH 96H 29/1200Z 25.3N 115.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 30/1200Z 26.7N 115.1W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER KIMBERLAIN