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Tropical Storm MIRIAM Forecast Discussion Number 19

Issued at 800 AM PDT WED SEP 26 2012

000
WTPZ43 KNHC 261449
TCDEP3
 
TROPICAL STORM MIRIAM DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
800 AM PDT WED SEP 26 2012
 
THE CLOUD PATTERN OF MIRIAM HAS BECOME POORLY ORGANIZED. THE CENTRAL
DENSE OVERCAST HAS DEGENERATED INTO A LONG BAND WRAPPING AROUND THE
WESTERN SIDE OF THE CIRCULATION. SATELLITE DATA ALSO INDICATE AN
INCREASING SEPARATION BETWEEN THE LOW- TO MID-LEVEL CENTERS DUE TO
20-25 KT OF SOUTHWESTERLY SHEAR ASSOCIATED WITH A SHORTWAVE TROUGH
ROTATING AROUND THE NORTHWESTERN SIDE OF THE STORM. SATELLITE
INTENSITY ESTIMATES RANGE FROM 55-65 KT...AND GIVEN THE
DETERIORATING SATELLITE APPEARANCE...THE INITIAL INTENSITY IS
LOWERED TO 55 KT. FURTHER GRADUAL WEAKENING IS LIKELY AS MIRIAM
ENCOUNTERS CONTINUED MODERATE OR STRONG SOUTHWESTERLY SHEAR...
GRADUALLY DECREASING SSTS...AND A DRIER AND MORE STABLE AIR MASS.
THE NHC INTENSITY FORECAST IS AN UPDATE OF THE PREVIOUS ONE AND IS
CLOSE TO THE SHIPS AND LGEM OUTPUT.
 
THE LONG-TERM INITIAL MOTION ESTIMATE IS 330/05...BUT RECENT
MICROWAVE DATA SUGGEST THAT THE SHORT-TERM MOTION COULD BE FARTHER
TO THE RIGHT. AS THE PREVIOUSLY MENTIONED SHORTWAVE TROUGH DIGS TO
THE WEST OF MIRIAM DURING THE NEXT DAY OR SO...THE CYCLONE SHOULD
MAINTAIN A SLOW NORTH-NORTHWESTWARD MOTION. A BEND OF THE TRACK
TOWARD THE NORTHWEST IS FORECAST WHEN THE SHORTWAVE REACHES A
POSITION TO THE SOUTH OF STORM IN 24-36 HOURS. IF MIRIAM DECOUPLES
SOONER THAN EXPECTED...THE LOW-LEVEL CENTER COULD MOVE MORE TO THE
LEFT THAN FORECAST. THE NHC TRACK FORECAST IS NEAR OR SLIGHTLY TO
THE LEFT OF THE PREVIOUS ONE AND IS CLOSE TO THE FSU
SUPERENSENSEMBLE AND THE MULTI-MODEL CONSENSUS THROUGH 24 HOURS AND
THEN CLOSE TO THE GFS AFTER THAT.
 
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/1500Z 20.0N 115.7W   55 KT  65 MPH
 12H  27/0000Z 20.9N 115.9W   45 KT  50 MPH
 24H  27/1200Z 22.0N 116.3W   40 KT  45 MPH
 36H  28/0000Z 22.6N 116.7W   35 KT  40 MPH
 48H  28/1200Z 23.0N 117.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  29/1200Z 23.2N 117.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  30/1200Z 23.4N 117.9W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  01/1200Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 

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