509 
 WTPZ43 KNHC 232032
 TCDEP3
  
 TROPICAL STORM MIRIAM DISCUSSION NUMBER   8
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
 200 PM PDT SUN SEP 23 2012
  
 MIRIAM APPEARS TO BE GRADUALLY STRENGTHENING.  THE CYCLONE IS
 MAINTAINING A CENTRAL DENSE OVERCAST WITH COLD CLOUD TOP
 TEMPEATURES. A 1554 UTC SSMIS PASS SHOWED A DEVELOPING MID-LEVEL
 EYE...AND A CLOSED LOW-LEVEL RING OF CONVECTION WAS EVIDENT IN AN
 EARLIER WINDSAT PASS.  IN ADDITION...TIGHTLY COILED BANDS DOMINATE
 THE OUTER CIRCULATION OF THE CYCLONE.  DVORAK T-NUMBERS ARE AT 3.5
 AND 4.0 FROM TAFB AND SAB...RESPECTIVELY...AND UW-CIMSS ADT CI
 VALUES ARE AT 4.4.  BASED ON A BLEND OF THE ABOVE DATA...THE
 INITIAL INTENSITY ESTIMATE IS RAISED TO 60 KT.
  
 SATELLITE AND MICROWAVE DATA SUGGEST THAT THE HEADING HAS BEEN
 SLIGHTLY TO THE LEFT OF THE PREVIOUS ESTIMATE. A LONGER-TERM
 AVERAGE OF FIXES SUGGESTS AN INITIAL MOTION ESTIMATE OF 300/08.
 GLOBAL MODELS SHOW CONTINUING WEST-NORTHWEST TO NORTHWEST MOTION AS
 MIRIAM ROUNDS THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE OVER
 NORTHERN MEXICO DURING THE NEXT 36 HOURS.  A GRADUAL TURN TOWARD
 THE NORTH-NORTHWEST AND NORTH ARE EXPECTED FROM 48-96 HOURS AS
 MIRIAM MOVES INTO A WEAKNESS ALONG 115W...CREATED BY A SHORTWAVE
 TROUGH PASSING THROUGH THE WESTERN UNITED STATES.  THE LATTER PART
 OF THE FORECAST PARTIALLY HINGES ON THE DEGREE OF INTERACTION WITH A
 MID- TO UPPER-LEVEL TROUGH FORECAST TO FORM WEST OR NORTHWEST OF
 MIRIAM.  THE SPREAD IN THE GUIDANCE IS STILL RATHER SIGNIFICANT...
 ESPECIALLY BEYOND 96 HOURS...BUT LITTLE CHANGE IS NOTED BETWEEN
 THIS CYCLE AND THE PREVIOUS ONE.  THE NHC TRACK FORECAST IS
 ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE...AND IS ON THE RIGHT
 SIDE OF THE GUIDANCE ENVELOPE...CLOSEST TO THE ECMWF/GFS SOLUTIONS.
  
 MIRIAM IS EXPECTED TO REMAIN IN A FAVORABLE ENVIROMENT FOR
 STRENGTHENING DURING THE NEXT 24 HOURS...AND THE RATE OF
 INTENSIFICATION COULD POTENTIALLY BE RAPID AS INDICATED BY THE
 SHIPS RI INDEX.  IN 2-3 DAYS...MIRIAM SHOULD CROSS THE UPPER-LEVEL
 RIDGE AXIS AND SHOULD ALSO INTERACT WITH A SHORTWAVE TROUGH DIVING
 SOUTHEASTWARD TOWARD THE CYCLONE.  AN INCREASE IN SHEAR RELATED TO
 THE ABOVE FACTORS AND GRADUALLY DECREASING SSTS SHOULD PROMOTE
 WEAKENING.  THE WEAKENING SHOULD CONTINUE DURING THE 3 TO 5 DAY
 PERIOD...WITH EVEN THE POSSIBILITY OF MIRIAM DECOUPLING ENTIRELY AS
 DEPICTED BY ECMWF. A CRITICAL ELEMENT OF THE INTENSITY FORECAST
 COULD BE THE LONGITUDE WHERE MIRIAM TURNS NORTHWARD...SINCE THE
 EXACT TRACK OF THE CYCLONE WITH RESPECT TO A STRONG GRADIENT IN
 SSTS COULD DETERMINE HOW QUICKLY THE CYCLONE WEAKENS.  THE NHC
 INTENSITY FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS AND IS IN
 GOOD AGREEMENT WITH THE LATEST INTENSITY CONSENSUS AIDS.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  23/2100Z 16.1N 110.5W   60 KT  70 MPH
  12H  24/0600Z 16.8N 111.8W   75 KT  85 MPH
  24H  24/1800Z 17.9N 113.4W   85 KT 100 MPH
  36H  25/0600Z 18.7N 114.5W   85 KT 100 MPH
  48H  25/1800Z 19.4N 115.2W   80 KT  90 MPH
  72H  26/1800Z 20.7N 115.9W   60 KT  70 MPH
  96H  27/1800Z 22.3N 116.0W   45 KT  50 MPH
 120H  28/1800Z 23.5N 116.0W   35 KT  40 MPH
  
 $$
 FORECASTER KIMBERLAIN