000 WTPZ43 KNHC 252046 TCDEP3 HURRICANE MIRIAM DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132012 200 PM PDT TUE SEP 25 2012 THE CLOUD PATTERN OF MIRIAM HAS DETERIORATED SIGNIFICANTLY DURING THE PAST FEW HOURS. THE COVERAGE AND INTENSITY OF DEEP CONVECTION HAS BEEN DECREASING...WHILE THE CENTRAL FEATURES OF THE CYCLONE HAVE BECOME LESS DISTINCT. UPPER-LEVEL WESTERLY FLOW ASSOCIATED WITH A DEVELOPING MID- TO UPPER-LEVEL LOW SEEN IN WATER VAPOR IMAGERY NEAR 26N111W IS ALREADY IMPINGING ON MIRIAM...WITH SHIPS AND UW-CIMSS SHEAR ANALYSES CURRENTLY DIAGNOSING 20 KT OF SOUTHWESTERLY SHEAR. DVORAK T-NUMBERS ARE AT 4.0 AND 4.5 FROM SAB AND TAFB...WHILE ADT CI VALUES ARE RUNNING A BIT HIGHER. THE INITIAL INTENSITY ESTIMATE IS LOWERED TO 75 KT IN AGREEMENT WITH THESE DATA. THE ABOVEMENTIONED UPPER-LEVEL TROUGH APPROACHING MIRIAM WILL PRODUCE PERSISTENT MODERATE TO STRONG SOUTHWESTERLY SHEAR OVER THE CYCLONE AS IT MOVES OVER GRADUALLY DECREASING SSTS. AS A RESULT... STEADY WEAKENING IS EXPECTED DURING THE NEXT 48 HOURS. AS THE SHEAR BECOMES MORE EXTREME BY DAY 3...THE GFS AND ECMWF DEPICT MIRIAM DECOUPLING AND LIKELY DISSIPATING BY DAY 5. THE NHC INTENSITY FORECAST IS REDUCED AGAIN COMPARED TO THE PREVIOUS ONE IN BEST AGREEMENT WITH THE SHIPS AND LGEM OUTPUT. GIVEN THE GOOD MODEL AGREEMENT...REMNANT LOW STATUS IS NOW INDICATED SOONER...ON DAY 3. THE INITIAL MOTION ESTIMATE IS 300/04. MIRIAM IS ABOUT TO TURN TOWARD THE NORTHWEST AROUND THE WESTERN EDGE OF A MID-LEVEL RIDGE EXTENDING FROM THE GULF OF MEXICO. A SLOW NORTH-NORTHWESTWARD MOTION SHOULD COMMENCE BY TOMORROW AND CONTINUE FOR THE NEXT COUPLE OF DAYS AS THE CYCLONE MOVES INTO A WEAKNESS ALONG 115W. THE MODEL GUIDANCE HAS SHIFTED WESTWARD THIS CYCLE IN THE SHORT TERM... PARTIALLY IN RESPONSE TO THE MORE WESTERLY INITIAL MOTION THAT HAS PERSISTED LONGER THAN EXPECTED. SINCE IT APPEARS THAT MIRIAM WILL BECOME A SHALLOW VORTEX SOONER THAN PREVIOUSLY EXPECTED...THE NHC TRACK HAS BEEN SHIFTED SOMEWHAT TO THE WEST OF THE PREVIOUS ONE. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 18.9N 114.9W 75 KT 85 MPH 12H 26/0600Z 19.6N 115.1W 65 KT 75 MPH 24H 26/1800Z 20.7N 115.4W 55 KT 65 MPH 36H 27/0600Z 21.9N 115.8W 45 KT 50 MPH 48H 27/1800Z 23.0N 116.0W 40 KT 45 MPH 72H 28/1800Z 24.2N 116.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 29/1800Z 25.5N 116.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 30/1800Z...DISSIPATED $$ FORECASTER KIMBERLAIN