693 
 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