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Tropical Storm MIRIAM Forecast Discussion Number 18

Issued at 200 AM PDT WED SEP 26 2012

000
WTPZ43 KNHC 260852
TCDEP3
 
TROPICAL STORM MIRIAM DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
200 AM PDT WED SEP 26 2012

THE CONVECTIVE ORGANIZATION OF MIRIAM HAS GONE RAPIDLY DOWNHILL OVER
THE PAST SEVERAL HOURS WITH MOST OF THE SIGNIFICANT THUNDERSTORM
ACTIVITY NORTH OF THE CENTER.  THE CENTRAL DENSE OVERCAST HAS ALSO
BECOME RATHER ELONGATED...AND AN EARLIER EYE FEATURE IS NO LONGER
APPARENT ON MICROWAVE DATA.  SATELLITE INTENSITY ESTIMATES RANGE
FROM 55-72 KT...AND GIVEN THE POOR SATELLITE APPEARANCE...THE
INITIAL WIND SPEED IS LOWERED TO 60 KT.  CONTINUED WEAKENING IS
LIKELY DUE TO MODERATE OR STRONG SOUTHWESTERLY SHEAR...GRADUALLY
COOLING SSTS...AND ENTRAINMENT OF A MORE STABLE AIRMASS.  THE NEW
FORECAST IS CLOSE TO A BLEND OF THE PREVIOUS ONE AND THE INTENSITY
CONSENSUS.  

AN UNCERTAIN INITIAL MOTION ESTIMATE IS 320/5.  ALMOST ALL THE
GUIDANCE MOVE MIRIAM TO THE NORTH OR NORTH-NORTHWEST TODAY IN
RESPONSE TO A DIGGING TROUGH SEEN ALONG 120W IN WATER VAPOR IMAGES. 
AS THE TROUGH DROPS SOUTH OF THE TROPICAL CYCLONE IN A DAY OR
TWO...MIRIAN WILL PROBABLY TURN TO THE NORTHWEST.  THE OFFICIAL
FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS ONE...CLOSE TO THE
FSU SUPERENSEMBLE...THROUGH 48 HOURS.  AFTER THAT TIME...LITTLE
MOTION IS INDICATED AS THE WEAK REMNANT SYSTEM WILL BE POSITIONED
IN LIGHT STEERING CURRENTS.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0900Z 19.5N 115.5W   60 KT  70 MPH
 12H  26/1800Z 20.3N 115.7W   50 KT  60 MPH
 24H  27/0600Z 21.5N 116.0W   45 KT  50 MPH
 36H  27/1800Z 22.4N 116.4W   35 KT  40 MPH
 48H  28/0600Z 22.9N 116.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  29/0600Z 23.2N 116.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  30/0600Z 23.5N 117.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  01/0600Z...DISSIPATED
 
$$
FORECASTER BLAKE
 

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