015 
 WTPZ43 KNHC 230232
 TCDEP3
  
 TROPICAL STORM MIRIAM DISCUSSION NUMBER   5
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
 800 PM PDT SAT SEP 22 2012
  
 MIRIAM HAS BECOME BETTER ORGANIZED OVER THE PAST SEVERAL HOURS.
 BANDING FEATURES ARE MORE DISTINCT TO THE NORTHEAST AND SOUTHWEST
 OF THE CENTER...AND CLOUD TOPS HAVE COOLED IN THE CENTRAL DENSE
 OVERCAST. DVORAK CI-NUMBERS WERE 2.5/35 KT FROM TAFB...3.0/45 KT
 FROM SAB...AND 3.3/51 KT FROM UW-CIMSS. SINCE EARLIER SCATTEROMETER
 DATA INDICATED THAT THE STORM WAS WEAKER THAN ITS SATELLITE
 PRESENTATION SUGGESTED...THE INITIAL WIND SPEED IS ONLY INCREASED
 TO 40 KT.
  
 THE ATMOSPHERIC AND OCEANIC CONDITIONS ARE EXPECTED TO BE QUITE
 CONDUCIVE FOR MIRIAM TO GAIN MORE STRENGTH DURING THE NEXT COUPLE
 OF DAYS. THE SHIPS RAPID INTENSIFICATION INDEX SHOWS MORE THAN A 50
 PERCENT CHANCE OF A 30-KT INTENSITY INCREASE DURING THE NEXT 24
 HOURS. THE NHC INTENSITY FORECAST LIES BETWEEN THE LOWER
 STATISTICAL GUIDANCE AND THE HIGHER DYNAMICAL MODELS...LEANING
 TOWARDS THE HIGHER END OF THE MODEL GUIDANCE FOR THE NEXT 48 HOURS.
 HOWEVER...IT WOULD NOT BE SUPRISING IF MIRIAM STRENGTHENS MORE THAN
 FORECAST. IN ABOUT 3 DAYS...MIRIAM IS EXPECTED TO BE MOVING OVER
 WATERS OF ABOUT 26C AND INTO MODERATE SOUTHWESTERLY WIND SHEAR.
 THESE LESS FAVORABLE CONDITIONS SHOULD END THE STRENGTHENING
 TREND...AND CAUSE THE CYCLONE TO WEAKEN.
  
 AFTER MOVING ERRATICALLY EARLIER TODAY...IT APPEARS THAT MIRIAM IS
 MOVING MORE STEADILY NOW. THE LATEST INITIAL MOTION ESTIMATE IS
 300/7. THE STORM SHOULD CONTINUE MOVING WEST-NORTHWESTWARD TO
 NORTHWESTWARD FOR THE NEXT COUPLE OF DAYS AS IT REMAINS STEERED BY
 A MID-LEVEL RIDGE TO ITS NORTHEAST. AFTER THAT TIME...THE TRACK
 BECOMES MUCH MORE UNCERTAIN. THE GFS...GFS ENSEMBLE MEAN...AND SOME
 OF THE HFIP GUIDANCE PREDICT MIRIAM TO TURN TO THE NORTH OR
 NORTH-NORTHEAST. CONVERSELY...THE ECMWF...HWRF...AND GFDL MODELS
 SHOW A TURN TO THE WEST BEYOND A COUPLE OF DAYS. IN ADDITION...THE
 LATEST SPREAD IN THE GFS ENSEMBLE MEMBERS IS ABOUT 1000 N MI BY DAY
 5. THE MAIN CAUSE OF THE LARGE MODEL DIVERGENCE APPEARS TO BE DUE
 TO DIFFERENCES IN THE POSITION OF A SHORTWAVE TROUGH OFF THE
 CALIFORNIA COAST AND THE VERTICAL DEPTH OF MIRIAM. OVERALL...THE
 MODEL GUIDANCE ENVELOPE HAS SHIFTED WESTWARD...AND THE OFFICIAL
 FORECAST HAS BEEN NUDGED IN THAT DIRECTION.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  23/0300Z 14.9N 108.5W   40 KT  45 MPH
  12H  23/1200Z 15.6N 109.6W   50 KT  60 MPH
  24H  24/0000Z 16.8N 111.3W   60 KT  70 MPH
  36H  24/1200Z 17.7N 112.9W   75 KT  85 MPH
  48H  25/0000Z 18.5N 114.3W   80 KT  90 MPH
  72H  26/0000Z 19.4N 116.0W   75 KT  85 MPH
  96H  27/0000Z 20.3N 117.0W   60 KT  70 MPH
 120H  28/0000Z 21.5N 118.0W   45 KT  50 MPH
  
 $$
 FORECASTER CANGIALOSI