661 
 WTPZ43 KNHC 231457
 TCDEP3
  
 TROPICAL STORM MIRIAM DISCUSSION NUMBER   7
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
 800 AM PDT SUN SEP 23 2012
  
 SATELLITE IMAGERY INDICATES THAT THE CLOUD PATTERN OF MIRIAM
 CONTINUES TO INCREASE IN ORGANIZATION.  A COMPACT CENTRAL DENSE
 OVERCAST HAS FORMED AND BECOME BETTER DEFINED DURING THE PAST 6-12
 HOURS.  THERE IS ALSO PLENTY OF COLD-TOPPED CONVECTION ASSOCIATED
 WITH THE CYCLONE...AND BANDING HAS BEEN INCREASING.  DVORAK
 T-NUMBERS HAVE INCREASED TO 3.5 FROM TAFB AND SAB...AND UW-CMSS ADT
 CI VALUES ARE AT 3.6.  BASED ON THESE DATA...THE INITIAL INTENSITY
 IS RAISED TO 55 KT.
  
 THE INITIAL MOTION ESTIMATE IS 305/07.  THE CYCLONE IS FORECAST TO
 MAINTAIN THIS GENERAL MOTION DURING THE NEXT DAY OR SO AS IT TURNS
 AROUND THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE LOCATED
 OVER NORTHERN MEXICO.  BY 48 HOURS...MIRIAM SHOULD ENCOUNTER A
 WEAKNESS ALONG 115W AS A LONGWAVE TROUGH DEVELOPS OVER THE WESTERN
 UNITED STATES.  THIS PATTERN SHOULD RESULT IN A GRADUAL NORTHWARD
 TURN AND A SLOWING OF THE FORWARD MOTION DURING THE 3 TO 5 DAY
 PERIOD.  THERE REMAINS A NOTABLE SPLIT IN THE GUIDANCE AFTER
 72 HOURS...PARTIALLY DUE TO THE DEGREE OF INTERACTION OF MIRIAM
 WITH A CUT-OFF LOW FORECAST TO DEVELOP WEST OF THE CYCLONE IN ABOUT
 4 DAYS.  THE NHC FORECAST HAS SHIFTED TOWARD THE EAST...FOLLOWING
 THE MULTI-MODEL CONSENSUS TVCE.  THE OFFICIAL FORECAST ALSO REMAINS
 ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE...BUT NOT AS FAR EAST AS
 THE ECMWF/GFS SOLUTIONS.
  
 MIRIAM SHOULD BE MOVING THROUGH AN ENVIRONMENT OF WARM SSTS...A VERY
 MOIST MID-TROPOSPHERE...AND LOW SHEAR DURING THE NEXT DAY OR SO. 
 THE SHIPS RAPID INTENSIFICATION INDEX RESPONDS TO THESE FAVORABLE
 PARAMETERS BY SHOWING A 75% CHANCE OF A 30 KT INCREASE IN STRENGTH
 DURING THE NEXT 24 HOURS. BY 72 HOURS...MIRIAM SHOULD BE NORTH OF
 THE UPPER-LEVEL RIDGE AXIS AND EXPERIENCE AN INCREASE IN WESTERLY
 SHEAR ALONG WITH GRADUALLY DECREASING SSTS.  WEAKENING IS EXPECTED
 AT THAT TIME...BUT THE RATE OF WEAKENING SEEMS DEPENDENT ON THE
 EXACT TRACK OF THE CYCLONE AS WELL AS ITS POTENTIAL INTERACTION
 WITH THE AFORMENTIONED CUT-OFF LOW. A TRACK FARTHER EAST COULD KEEP
 MIRIAM OVER WARMER WATER LONGER AND AWAY FROM EVEN STRONGER SHEAR
 CONDITIONS ASSOCIATED WITH THE CUT-OFF LOW. THE NHC INTENSITY
 FORECAST IS INCREASED A BIT IN THE SHORT TERM RELATIVE TO THE
 PREVIOUS ONE BUT IS CLOSE TO THE INTENSITY CONSENSUS AIDS.
   
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  23/1500Z 15.6N 109.6W   55 KT  65 MPH
  12H  24/0000Z 16.5N 110.8W   70 KT  80 MPH
  24H  24/1200Z 17.6N 112.4W   85 KT 100 MPH
  36H  25/0000Z 18.5N 113.7W   85 KT 100 MPH
  48H  25/1200Z 19.0N 114.5W   80 KT  90 MPH
  72H  26/1200Z 20.2N 115.5W   70 KT  80 MPH
  96H  27/1200Z 21.4N 116.0W   55 KT  65 MPH
 120H  28/1200Z 22.5N 116.0W   40 KT  45 MPH
  
 $$
 FORECASTER KIMBERLAIN