000
AXPZ20 KNHC 242142
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC MON SEP 24 2012

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...SPECIAL FEATURES...
HURRICANE MIRIAM AT 18.1N 113.5W AT 2100 UTC MOVING NW OR 305 
DEG AT 8 KT.  ESTIMATED MINIMUM CENTRAL PRES 960 MB.  MAXIMUM 
SUSTAINED WIND SPEED 105 GUSTS TO 130 KT.  MODEL GUIDANCE 
SUGGEST THAT MIRIAM MAY HAVE PEAKED ITS STRENGTHENING CYCLE AND 
IS EXPECTED TO START A DOWNWARD TREND AS SEA SURFACE TEMPERATURE 
START COOLING AND SW WIND SHEAR INCREASES.  MIRIAM HAS NUMEROUS 
STRONG CONVECTION FROM 16N-21N BETWEEN 110W-115W. SEE LATEST NHC 
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC 
FOR MORE DETAILS.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH FROM 10N85W TO 11N95W TO 10N104W...THEN RESUMES 
FROM 15N117W TO 11N125W THEN ITCZ 09N140W.  SCATTERED MODERATE 
CONVECTION WITHIN 200 NM OF AXIS E OF 108W AND WITHIN 90 NM S 
OF AXIS W OF 130W.

...DISCUSSION...
WELL DEFINED UPPER LEVEL CYCLONE AT 32N143W THAT PROVIDED STRONG 
SUPPORT ALOFT FOR COLD FRONT NEAR NW CORNER OF BASIN SHIFTED N 
WHILE FRONT BECAME STATIONARY.  FRONT NOW BECOMING DIFFUSE AND 
BLOCKED FROM FURTHER EASTWARD MOVE BY 1027 MB HIGH PRES AT 
37N138W.  NEVERTHELESS...LARGE LONG PERIOD NW SWELLS GENERATED 
BY FRONT SPREAD INTO CORNER OF BASIN AND PROPAGATE TO COVER MOST 
OF BASIN W OF 110W BY LATE WED.  SEAS BUILD TO 9-12 FT...EXCEPT 
HIGHER ASSOCIATED WITH HURRICANE MIRIAM.    

BROAD UPPER LEVEL ANTICYCLONE AT 16N106W JUST SE OF HURRICANE 
MIRIAM MAINTAINS LIGHT WIND SHEAR ALOFT AND GOOD DIVERGENT 
OUTFLOW FOR MIRIAM THAT HAS ALLOWED MIRIAM TO INTENSIFY.  THESE 
FAVORABLE CONDITIONS MITIGATE AS MIRIAM CONTINUES MOVING NW AWAY 
FROM ANTICYCLONE AND START FEELING HIGHER SEA SURFACE 
TEMPERATURES. 

N WINDS OVER GULF OF TEHUANTEPEC HAVE WEAKENED TO A FRESH BREEZE 
AND EXPECTED TO FURTHER DIMINISH BY EARLY TUE. 

$$
WALLY BARNES