728 
 WTPZ43 KNHC 230843
 TCDEP3
  
 TROPICAL STORM MIRIAM DISCUSSION NUMBER   6
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
 200 AM PDT SUN SEP 23 2012
  
 MIRIAM HAS CONTINUED TO BECOME BETTER ORGANIZED SINCE THE PREVIOUS
 ADVISORY...ESPECIALLY DURING THE PAST COUPLE OF HOURS. A SMALL CDO
 FEATURE HAS DEVELOPED OVER THE CENTER AND CONVECTIVE BANDING HAS
 ALSO BECOME MORE PRONOUNCED. SATELLITE INTENSITY ESTIMATES ARE A
 CONSENSUS T3.0/45 KT FROM TAFB AND SAB...AND RECENT UW-CIMSS ADT
 VALUES WERE T3.5/55 KT. BASED ON THESE DATA...THE INITIAL INTENSITY
 IS INCREASED TO 45 KT. UPPER-LEVEL OUTFLOW IS GOOD IN ALL
 QUADRANTS...AND CONTINUES TO EXPAND AND BECOME MORE SYMMETRICAL.
 
 MICROWAVE SATELLITE IMAGERY OVER THE PAST 6 HOURS INDICATES THE
 CENTER HAS DEVELOPED A LITTLE FARTHER TO THE NORTHEAST OF THE
 PREVIOUS ADVISORY TRACK...AND THE INITIAL MOTION ESTIMATE IS NOW
 310/07 KT. MIRIAM IS EXPECTED TO MOVE NORTHWESTWARD AROUND A
 DEEP-LAYER SUBTROPICAL RIDGE FOR THE NEXT 72 HOURS. BY DAYS 4 AND
 5...HOWEVER...THE TRACK FORECAST BECOMES A LITTLE MORE UNCERTAIN
 DUE TO A LARGE SPREAD IN THE MODEL GUIDANCE. THE NEW 23/00Z ECMWF
 MODEL MADE A MAJOR TRACK SHIFT TO THE EAST AND IS NOW THE RIGHTMOST
 OF ALL THE MODEL GUIDANCE...WHICH IS MORE IN LINE WITH THE PREVIOUS
 GFS MODEL RUNS. IN CONTRAST...THE HWRF AND GFDL MODELS HAVE
 CONTINUED THEIR MORE WESTWARD MOTION IN THE LATTER PERIODS. GIVEN
 THAT MIRIAM IS EXPECTED TO BECOME A FAIRLY ROBUST HURRICANE BY 72
 HOURS...THE OFFICIAL FORECAST TRACK HAS BEEN SHIFTED TO THE RIGHT
 OF THE PREVIOUS ADVISORY TRACK...AND FOLLOWS THE TREND OF THE GFS
 AND ECMWF MODELS SINCE BOTH OF THOSE MODELS DEVELOP A DEEPER VORTEX
 THAT IS LIFTED NORTHWARD ON DAYS 4 AND 5 BY A SHORTWAVE TROUGH
 FORECAST TO DIG SOUTHWARD TO THE WEST OF BAJA CALIFORNIA.
  
 ENVIRONMENTAL CONDITIONS ARE FORECAST TO BE QUITE FAVORABLE FOR
 ADDITIONAL STRENGTHENING TO OCCUR FOR AT LEAST THE NEXT 48 HOURS.
 IN FACT...WITH VERTICAL SHEAR VALUES ARE EXPECTED TO REMAIN BELOW 
 5 KT FOR THE NEXT 36 HOURS...AND IT WOULD NOT SURPRISE ME IF RAPID
 INTENSIFICATION OCCURS AT SOME POINT DURING THAT TIME PERIOD. DUE
 TO MIRIAM FORECAST TO BE FARTHER EAST AND OVER WARMER WATERS THAN
 PREVIOUS EXPECTED ON DAYS 4 AND 5...THE INTENSITY WAS NUDGED UPWARD
 SLIGHTLY AT THOSE LATTER TIME PERIODS...AND MIGHT NEED TO BE
 INCREASED ON SUBSEQUENT ADVISORIES IF A FURTHER EASTWARD SHIFT IN
 THE FORECAST IS WARRANTED. THE OFFICIAL INTENSITY FORECAST IS
 SIMILAR TO BUT SLIGHTLY HIGHER THAN THE HWRF AND FSSE MODELS...
 BOTH OF WHICH ARE ABOVE THE REMAINING NHC INTENSITY GUIDANCE.
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  23/0900Z 15.3N 108.8W   45 KT  50 MPH
  12H  23/1800Z 16.2N 110.1W   55 KT  65 MPH
  24H  24/0600Z 17.2N 111.7W   65 KT  75 MPH
  36H  24/1800Z 18.1N 113.2W   75 KT  85 MPH
  48H  25/0600Z 18.7N 114.3W   85 KT 100 MPH
  72H  26/0600Z 19.8N 115.7W   75 KT  85 MPH
  96H  27/0600Z 20.8N 116.5W   65 KT  75 MPH
 120H  28/0600Z 21.8N 117.0W   55 KT  65 MPH
  
 $$
 FORECASTER STEWART