000
WTPZ43 KNHC 241450
TCDEP3
 
HURRICANE MIRIAM DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
800 AM PDT MON SEP 24 2012
 
THE RAPID INTENSIFICATION PHASE THAT MIRIAM HAS BEEN UNDERGOING
CONTINUES.  THE HURRICANE HAS MAINTAINED A COMPACT AND FAIRLY
SYMMETRIC CENTRAL DENSE OVERCAST WITH VERY COLD CLOUD TOP
TEMPERATURES DURING THE PAST SEVERAL HOURS. A PINHOLE EYE...EVIDENT
IN FIRST-LIGHT VISIBLE IMAGERY...HAS ALSO BEEN WARMING. A 0829 UTC
TRMM PASS SUGGESTED THAT AN OUTER EYEWALL COULD BE FORMING AT A
LARGE RADIUS...BUT THERE ARE NO SIGNS OF IT CONTRACTING.  DVORAK
T-NUMBERS ARE 5.5 AND 5.0 FROM SAB AND TAFB...RESPECTIVELY...AND THE
LATEST ADT CI VALUES ARE 5.8.  A BLEND OF THESE DATA YIELD AN
INITIAL INTENSITY ESTIMATE OF 105 KT.
 
THE EYE OF MIRIAM HAS BEEN WOBBLING DURING THE PAST SEVERAL HOURS.
SMOOTHING THROUGH THESE WOBBLES GIVES AN INITIAL MOTION ESTIMATE OF
OF 305/10.  MIRIAM IS ABOUT TO MOVE AROUND WESTERN EDGE OF A MID-
LEVEL RIDGE OVER NORTHERN MEXICO AND INTO A WEAKNESS ALONG 115W. 
THIS SYNOPTIC PATTERN SHOULD RESULT IN A GRADUAL NORTHWARD TURN AND
A REDUCTION IN FORWARD SPEED DURING THE NEXT FEW DAYS. AS A MID-/
UPPER-LEVEL CYCLONE FORMS OFFSHORE OF THE SOUTHERN CALIFORNA COAST
ON DAYS 4-5 AND SLIDES EASTWARD...MIRIAM SHOULD BE PUSHED NORTH-
NORTHEASTWARD OR EVEN NORTHEASTWARD.  THE NHC TRACK FORECAST IS
LARGELY UNCHANGED RELATIVE TO THE PREVIOUS ONE.  THE FORECAST
REMAINS ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE...HEAVILY
WEIGHTED TOWARD THE GFS/ECMWF.
 
BARRING AN EYEWALL REPLACEMENT...MIRIAM COULD STILL INTENSIFY A
BIT MORE DURING THE NEXT 12-24 HOURS IN A LOW SHEAR ENVIRONMENT AND
OVER WARM WATERS.  A GRADUAL DECAY IS LIKELY FROM 24-48 HOURS AS
MIRIAM MOVES OVER MARGINALLY WARM WATERS...FOLLOWED BY A STEADIER
DECLINE AFTER THAT AS MIRIAM ENCOUNTERS AN INCREASE IN UPPER-LEVEL
WESTERLY FLOW.  BY DAYS 4-5...A FURTHER INCREASE IN WESTERLY SHEAR
IS EXPECTED AS MIRIAM INTERACTS WITH THE CLOSED LOW TO ITS WEST. 
THIS SHOULD LEAD TO A MORE RAPID WEAKENING AND PERHAPS A DECOUPLING
OF THE CYCLONE...AS DEPICTED IN THE ECWMF.  ALTHOUGH THE NHC
INTENSITY FORECAST IS GENERALLY ABOVE THE GUIDANCE...IT IS LOWER
COMPARED TO THE PREVIOUS ADVISORY FROM DAYS 3-5.
 

FORECAST POSITIONS AND MAX WINDS
 
INIT  24/1500Z 17.7N 112.9W  105 KT 120 MPH
 12H  25/0000Z 18.4N 113.8W  110 KT 125 MPH
 24H  25/1200Z 19.1N 114.6W  105 KT 120 MPH
 36H  26/0000Z 19.9N 114.9W   95 KT 110 MPH
 48H  26/1200Z 20.9N 115.1W   85 KT 100 MPH
 72H  27/1200Z 22.8N 115.3W   65 KT  75 MPH
 96H  28/1200Z 24.8N 114.8W   50 KT  60 MPH
120H  29/1200Z 26.1N 113.7W   35 KT  40 MPH
 
$$
FORECASTER KIMBERLAIN