000 WTPZ43 KNHC 260257 TCDEP3 HURRICANE MIRIAM DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132012 800 PM PDT TUE SEP 25 2012 MODERATE SOUTHWESTERLY VERTICAL SHEAR IS CONTINUING TO TAKE ITS TOLL ON MIRIAM THIS EVENING. THE CONVECTION IS LOSING ITS CENTRAL DENSE OVERCAST AND BEGINNING TO SHOW MORE OF A SHEAR PATTERN. DVORAK CURRENT INTENSITY ESTIMATES ARE AT 77 KT FROM TAFB AND 65 KT FROM SAB WHILE A 2214Z AMSU INTENSITY ESTIMATE FROM CIMSS WAS 72 KT. A BLEND OF THESE GIVES 70 KT AT THE ADVISORY TIME. TWO FORTUITOUS AMSU AND SSMIS MICROWAVE PASSES PROVIDE A RELATIVELY CONFIDENT ESTIMATE THAT THE MOTION OF MIRIAM IS NEAR 310/4. THE CYCLONE IS CURRENTLY BEING STEERED PRIMARILY BY THE INFLUENCE OF A WEAK DEEP-LAYER RIDGE TO ITS EAST. A CONTINUED SLOW MOVEMENT TOWARD THE NORTH-NORTHWEST OR NORTH IS EXPECTED FOR THE NEXT TWO DAYS. AS THE SYSTEM TRANSFORMS INTO A REMNANT LOW...IT SHOULD TURN TOWARD THE NORTHWEST WHILE BEING ADVECTED ALONG IN THE LOW-LEVEL FLOW. THE TRACK PREDICTION IS SLIGHTLY SLOWER AND A BIT TO THE WEST OF THE PREVIOUS ADVISORY. THE NEW FORECAST IS ALSO CLOSE TO THE TRACK CONSENSUS EXCLUDING THE UKMET...AS THIS MODEL HAS AN UNREALISTICALLY SLOW SPEED IN COMPARISON TO ALL OF THE REMAINING GUIDANCE. MIRIAM SHOULD CONTINUE TO GRADUALLY WEAKEN UNDER THE COMBINED INFLUENCE OF MODERATE VERTICAL SHEAR...COOLING SSTS AND A MORE STABLE ATMOSPHERE. THE CYCLONE SHOULD BECOME A REMNANT LOW AROUND THREE DAYS AS THE SSTS BY THAT TIME SHOULD BE AROUND 24C. THE INTENSITY PREDICTION IS CLOSEST TO THE LGEM AND SHIPS STATISTICAL MODELS AND IS VERY SIMILAR TO THAT OF THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 19.1N 115.2W 70 KT 80 MPH 12H 26/1200Z 19.8N 115.6W 60 KT 70 MPH 24H 27/0000Z 21.0N 115.7W 50 KT 60 MPH 36H 27/1200Z 22.2N 116.2W 40 KT 45 MPH 48H 28/0000Z 22.9N 116.5W 35 KT 40 MPH 72H 29/0000Z 23.5N 117.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/0000Z 24.0N 117.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/0000Z...DISSIPATED $$ FORECASTER LANDSEA