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Tropical Storm MIRIAM Forecast Discussion Number 20

Issued at 200 PM PDT WED SEP 26 2012

000
WTPZ43 KNHC 262035
TCDEP3
 
TROPICAL STORM MIRIAM DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
200 PM PDT WED SEP 26 2012
 
SATELLITE IMAGES INDICATE THAT MIRIAM CONTINUES TO WEAKEN...AS THE
20-25 KT OF SOUTHWESTERLY SHEAR DIAGNOSED OVER THE CYCLONE IS
GRADUALLY TAKING A TOLL.  INNER CORE CONVECTION IS MINIMAL...AND
DEEP CONVECTION IN A BAND WRAPPING AROUND THE PERIPHERY OF THE
CIRCULATION HAS WARMED CONSIDERABLY DURING THE PAST SEVERAL HOURS.   
DVORAK T-NUMBERS ARE SLOWLY DECREASING...AND A BLEND OF T-
AND CI-NUMBERS IS USED TO ARRIVE AT THE INITIAL INTENSITY ESTIMATE
OF 50 KT.
 
NO DECREASE IN THE SOUTHWESTERLY TO WEST-SOUTHWESTERLY SHEAR IS
PREDICTED DURING THE NEXT COUPLE OF DAYS.  THE COMBINATION OF THE
SHEAR...PROGRESSIVELY COOLER WATERS...AND THE ENTRAINMENT OF A
SUBSTANTIALLY DRIER AND MORE STABLE AIR MASS SHOULD PROMOTE
ADDITIONAL WEAKENING.  THE NHC INTENSITY FORECAST IS JUST ABOUT THE
SAME AS THE PREVIOUS ONE...AND IS LINE WITH THE SHIPS...LGEM...
AND INTENSITY CONSENSUS AIDS.  REMNANT LOW STATUS IS INDICATED IN 48
HOURS...THOUGH IT COULD OCCUR SOONER.
 
MICROWAVE DATA AND VISIBLE SATELLITE IMAGERY WERE USED TO MAKE AN
EASTWARD RELOCATION OF THE CENTER....AND HAVE BEEN HELPFUL IN
ESTABLISHING A MORE CONFIDENT INITIAL MOTION OF 350/06. SO LONG AS 
AS THE CIRCULATION OF MIRIAM MAINTAINS VERTICAL INTEGRITY...THE
CYCLONE SHOULD MOVE CYCLONICALLY AROUND A PIECE OF AN UPPER-LEVEL
TROUGH CURRENTLY ROTATING AROUND THE STORM. AS THE CYCLONE BECOMES
MORE SHALLOW IN NATURE AND RESPONDS TO THE LOW- LEVEL FLOW...A
WESTWARD BEND IS ANTICIPATED. THIS BEND COULD EVEN BE TOWARD THE
SOUTHWEST OR SOUTH-SOUTHWEST...AS DEPICTED IN SEVERAL MODEL
SOLUTIONS. THE NHC TRACK IS ADJUSTED SLIGHTLY TO THE LEFT AFTER 24
HOURS...NEAR BUT TO THE NORTH OF THE MULTI-MODEL CONSENSUS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 20.8N 115.4W   50 KT  60 MPH
 12H  27/0600Z 21.6N 115.6W   45 KT  50 MPH
 24H  27/1800Z 22.4N 116.1W   35 KT  40 MPH
 36H  28/0600Z 22.8N 116.5W   30 KT  35 MPH
 48H  28/1800Z 22.9N 116.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  29/1800Z 22.9N 117.2W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  30/1800Z 22.9N 117.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  01/1800Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 

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