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Tropical Storm MIRIAM Forecast Discussion Number 21

Issued at 800 PM PDT WED SEP 26 2012

000
WTPZ43 KNHC 270232
TCDEP3
 
TROPICAL STORM MIRIAM DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
800 PM PDT WED SEP 26 2012
 
CONVECTIVE CLOUD TOPS CONTINUE TO WARM...AND DEEP CONVECTION IS
LIMITED TO A BAND LOCATED ABOUT 150 N MI TO THE NORTH OF THE
CENTER.  DVORAK NUMBERS HAVE DROPPED TO T3.0/4.0 FROM TAFB AND
T2.0/3.0 FROM SAB.  BASED ON A BLEND OF THE FINAL-T AND CI
NUMBERS...THE ADVISORY INTENSITY IS SET AT 40 KT.  THIS IS
SUPPORTED BY A CI NUMBER OF 2.8 FROM THE LATEST UW-CIMSS ADT
ESTIMATE.

MIRIAM WILL CONTINUE TO BE AFFECTED BY 20-25 KT OF DEEP-LAYER
WEST-SOUTHWESTERLY SHEAR IN THE COMING DAYS...AND THE CENTER IS
BEGINNING TO MOVE OVER WATER THAT IS COLDER THAN 26C.  THIS
ENVIRONMENT IS NOT LIKELY TO SUPPORT SIGNIFICANT DEEP CONVECTION...
AND MIRIAM COULD BECOME POST-TROPICAL AS EARLY AS THURSDAY IF
CURRENT CONVECTIVE TRENDS HOLD.  THE NHC INTENSITY FORECAST FOLLOWS
THE SAME WEAKENING SHOWN BY THE STATISTICAL GUIDANCE...AND MOST OF
THE GLOBAL MODELS DISSIPATE THE REMNANT LOW IN ABOUT 5 DAYS.

MIRIAM IS MOVING NORTH-NORTHWESTWARD AT ABOUT 6 KT AS IT ROTATES
AROUND A MID-TROPOSPHERIC LOW LOCATED NOT TOO FAR TO ITS WEST.  THE
CYCLONE WILL SOON BE RUNNING INTO A LARGE AREA OF HIGH PRESSURE
CENTERED TO THE WEST OF CALIFORNIA...AND IT IS LIKELY TO BEGIN
MOVING SLOWLY WESTWARD OR EVEN SOUTHWESTWARD AFTER 48 HOURS. 
ALMOST ALL THE TRACK MODELS SHOW THE HIGH PRESSURE PUSHING MIRIAM
SOUTHWARD BEFORE IT DISSIPATES...AND THAT SCENARIO IS INDICATED IN
THE OFFICIAL FORECAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0300Z 21.5N 115.7W   40 KT  45 MPH
 12H  27/1200Z 22.2N 116.1W   35 KT  40 MPH
 24H  28/0000Z 22.7N 116.6W   30 KT  35 MPH
 36H  28/1200Z 22.8N 117.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  29/0000Z 22.9N 117.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  30/0000Z 22.9N 117.6W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  01/0000Z 22.5N 118.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  02/0000Z...DISSIPATED
 
$$
FORECASTER BERG
 

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