269 
 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