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Hurricane MIRIAM Forecast Discussion Number 17

Issued at 800 PM PDT TUE SEP 25 2012

000
WTPZ43 KNHC 260257
TCDEP3
 
HURRICANE MIRIAM DISCUSSION NUMBER  17
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
800 PM PDT TUE SEP 25 2012
 
MODERATE SOUTHWESTERLY VERTICAL SHEAR IS CONTINUING TO TAKE ITS TOLL
ON MIRIAM THIS EVENING. THE CONVECTION IS LOSING ITS CENTRAL DENSE
OVERCAST AND BEGINNING TO SHOW MORE OF A SHEAR PATTERN. DVORAK
CURRENT INTENSITY ESTIMATES ARE AT 77 KT FROM TAFB AND 65 KT FROM
SAB WHILE A 2214Z AMSU INTENSITY ESTIMATE FROM CIMSS WAS 72 KT. A
BLEND OF THESE GIVES 70 KT AT THE ADVISORY TIME. 

TWO FORTUITOUS AMSU AND SSMIS MICROWAVE PASSES PROVIDE A RELATIVELY
CONFIDENT ESTIMATE THAT THE MOTION OF MIRIAM IS NEAR 310/4. THE
CYCLONE IS CURRENTLY BEING STEERED PRIMARILY BY THE INFLUENCE OF A
WEAK DEEP-LAYER RIDGE TO ITS EAST. A CONTINUED SLOW MOVEMENT TOWARD
THE NORTH-NORTHWEST OR NORTH IS EXPECTED FOR THE NEXT TWO DAYS. AS
THE SYSTEM TRANSFORMS INTO A REMNANT LOW...IT SHOULD TURN TOWARD
THE NORTHWEST WHILE BEING ADVECTED ALONG IN THE LOW-LEVEL FLOW. THE
TRACK PREDICTION IS SLIGHTLY SLOWER AND A BIT TO THE WEST OF THE
PREVIOUS ADVISORY. THE NEW FORECAST IS ALSO CLOSE TO THE TRACK
CONSENSUS EXCLUDING THE UKMET...AS THIS MODEL HAS AN
UNREALISTICALLY SLOW SPEED IN COMPARISON TO ALL OF THE REMAINING
GUIDANCE.

MIRIAM SHOULD CONTINUE TO GRADUALLY WEAKEN UNDER THE COMBINED
INFLUENCE OF MODERATE VERTICAL SHEAR...COOLING SSTS AND A MORE
STABLE ATMOSPHERE.  THE CYCLONE SHOULD BECOME A REMNANT LOW AROUND
THREE DAYS AS THE SSTS BY THAT TIME SHOULD BE AROUND 24C.  THE
INTENSITY PREDICTION IS CLOSEST TO THE LGEM AND SHIPS STATISTICAL
MODELS AND IS VERY SIMILAR TO THAT OF THE PREVIOUS ADVISORY.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0300Z 19.1N 115.2W   70 KT  80 MPH
 12H  26/1200Z 19.8N 115.6W   60 KT  70 MPH
 24H  27/0000Z 21.0N 115.7W   50 KT  60 MPH
 36H  27/1200Z 22.2N 116.2W   40 KT  45 MPH
 48H  28/0000Z 22.9N 116.5W   35 KT  40 MPH
 72H  29/0000Z 23.5N 117.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  30/0000Z 24.0N 117.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  01/0000Z...DISSIPATED
 
$$
FORECASTER LANDSEA
 

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