Hurricane MIRIAM

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HURRICANE MIRIAM DISCUSSION NUMBER  12...CORRECTED
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
200 PM PDT MON SEP 24 2012
 
CORRECTED STATUS AT DAY 5

THE INTENSIFICATION PHASE THAT MIRIAM HAS BEEN UNDERGOING HAS COME
TO AN END...AS THERE HAS BEEN A DEGRADATION IN THE SATELLITE
APPEARANCE OF THE CYCLONE IN THE LAST FEW HOURS. CLOUD TOP
TEMPERATURES HAVE GRADUALLY BEEN WARMING AND THE EYE HAS BECOME
LESS DISTINCT.  A 1640 UTC TRMM IMAGE INDICATED THAT AN EYEWALL
REPLACEMENT COULD BE UNDERWAY...WITH A SMALL INNER EYEWALL EVIDENT
AND AN OUTER EYEWALL HAVING CONTRACTED SLIGHTLY TO A RADIUS OF 50 N
MI. DVORAK T-NUMBERS HAVE LEVELED OFF AT 5.5 FROM BOTH SATELLITE
AGENCIES...AND UW-CIMSS ADT CI VALUES HAVE DECREASED TO 5.6. THE
INITIAL INTENSITY ESTIMATE IS HELD AT 105 KT...IN AGREEMENT WITH
THESE DATA.
 
THE EYE OF MIRIAM HAS WOBBLED A BIT TO THE LEFT DURING THE LAST FEW
HOURS...AND HAS SLOWED IN FORWARD SPEED.  A LONGER-TERM AVERAGE OF
CENTER FIXES GIVES AN INITIAL MOTION ESTIMATE OF 305/08.  MIRIAM
SHOULD CONTINUE ON A SLOWER NORTHWESTWARD COURSE FOR THE NEXT DAY
OR SO AS IT ROUNDS THE SOUTHWESTERN SIDE OF A MID-LEVEL RIDGE OVER
NORTHERN MEXICO.  AFTER THAT TIME...MIRIAM SHOULD MOVE INTO A
WEAKNESS ALONG 115W AND TURN NORTHWARD FOR A COUPLE OF DAYS.  THE
INFLUENCE OF A MID- TO UPPER-LEVEL LOW FORMING OFFSHORE OF THE
SOUTHERN CALIFORNIA COAST FROM DAYS 3-5 SHOULD PUSH THE TRACK OF
MIRIAM NORTH-NORTHEASTWARD...OR EVEN NORTHEASTWARD...DURING THAT
TIME.  NO SUBSTANTIVE CHANGES WERE MADE TO THE PREVIOUS
FORECAST...WHICH IS WEIGHTED HEAVILY ON A BLEND OF THE ECMWF AND
GFS MODELS.  AS IN PREVIOUS OFFICIAL FORECASTS...THIS IS NEAR THE
RIGHT SIDE OF THE GUIDANCE ENVELOPE.
 
IT IS UNCLEAR AS TO WHETHER THE CURRENT EYEWALL REPLACEMENT WILL
CONTINUE.  IN ANY EVENT...A COMPLETION OF THE EYEWALL REPLACEMENT
CYCLE IS NOT LIKELY TO OCCUR BEFORE MIRIAM REACHES MARGINALLY WARM
WATERS AND SOME INCREASE IN WESTERLY SHEAR IN ABOUT 24 HOURS.
WEAKENING IS EXPECTED DURING THE INTERIM AND AFTERWARDS AS THE
CYCLONE MOVES CLOSE TO A STRONG GRADIENT OF SSTS AND EXPERIENCES
MODERATE WESTERLY SHEAR.  A FURTHER INCREASE IN WESTERLY SHEAR
ASSOCIATED THE ABOVEMENTIONED CLOSED MID- TO UPPER-LEVEL CYCLONE TO
THE WEST OF MIRIAM WILL LIKELY OCCUR LATE IN THE PERIOD.  THERE IS
NOW A GENERAL AGREEMENT OF BOTH THE ECWMF AND GFS GUIDANCE THAT
THIS WILL RESULT IN A DECOUPLING OF THE CYCLONE AND A RAPID
WEAKENING.  THE NHC INTENSITY FORECAST HAS BEEN REDUCED RELATIVE TO
THE PREVIOUS ONE...REPRESENTING AN AVERAGE OF THE SHIPS/LGEM AND
THE LATEST INTENSITY CONSENSUS AIDS.  REMNANT LOW STATUS IN
INDICATED ON DAY 5.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/2100Z 18.1N 113.5W  105 KT 120 MPH
 12H  25/0600Z 18.5N 114.2W  100 KT 115 MPH
 24H  25/1800Z 19.3N 114.8W   90 KT 105 MPH
 36H  26/0600Z 20.1N 115.0W   80 KT  90 MPH
 48H  26/1800Z 21.1N 115.1W   70 KT  80 MPH
 72H  27/1800Z 23.4N 115.2W   55 KT  65 MPH
 96H  28/1800Z 25.5N 114.4W   40 KT  45 MPH
120H  29/1800Z 27.5N 113.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER KIMBERLAIN
 
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