000
AXPZ20 KNHC 240928
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0845 UTC.

...SPECIAL FEATURES...
HURRICANE MIRIAM CENTERED NEAR 17.3N 112.2W AT 24/0900 UTC 
MOVING NW OR 305 DEGREES AT 11 KT. THIS GENERAL MOTION WITH A 
REDUCTION IN FORWARD SPEED IS EXPECTED DURING THE NEXT COUPLE OF 
DAYS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 971 MB. MAXIMUM 
SUSTAINED WIND SPEED IS 90 KT GUSTS TO 110 KT. MIRIAM IS NOW A 
CATEGORY TWO HURRICANE ON THE SAFFIR-SIMPSON HURRICANE WIND 
SCALE. ADDITIONAL STRENGTHENING IS FORECAST DURING THE NEXT DAY 
OR SO...AND MIRIAM COULD BECOME A MAJOR HURRICANE LATER TODAY AS 
IT IS EXPECTED TO REMAIN OVER SEA SURFACE TEMPERATURES OF 27-28C 
AND IN A FAVORABLE UPPER-LEVEL WIND PATTERN. NUMEROUS STRONG 
CONVECTION IS NOTED WITHIN 75 NM OF CENTER. SCATTERED MODERATE 
TO STRONG CONVECTION IS SEEN ELSEWHERE FROM 14N TO 19N BETWEEN 
110W AND 114W. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO 
HEADERS MIATCMEP3/WTPZ23 KNHC FOR MORE DETAILS.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH EXTENDS FROM 10N86W TO 09N100W...THEN RESUMES W 
OF HURRICANE MIRIAM FROM 12N114W TO 10N124W. THE ITCZ CONTINUES 
FROM 10N124W TO BEYOND 09N140W. SCATTERED MODERATE CONVECTION 
CAN BE FOUND WITHIN 100 NM S OF ITCZ AXIS BETWEEN 131W AND 136W.

...DISCUSSION...
ALOFT...AN UPPER TROUGH EXTENDS FROM THE SOUTHERN CALIFORNIA 
COAST TO A CUT OFF LOW NEAR 31N143W...WITH SW TO S WINDS OF 
40-50 KT TRANSPORTING MID TO UPPER LEVEL MOISTURE ACROSS THE NW 
CORNER OF THE FORECAST REGION. A BROAD ANTICYCLONE CENTERED NEAR 
ACAPULCO MEXICO EXTENDS A RIDGE E TO W BETWEEN 90W AND 130W. 
THIS FLOW CONTINUES TO YIELD A LOW SHEAR ENVIRONMENT FOR 
STRENGTHENING HURRICANE MIRIAM. NE TO E FLOW ALOFT DOMINATES THE 
WATERS E OF 120W. ANOTHER WEAKER ANTICYCLONE IS NEAR 11N138W.  
AN INVERTED TROUGH ALONG 132W S OF 12N CAN BE SEEN SEPARATING 
THE TWO RIDGES.  

AT LOW LEVELS...A 1027 MB HIGH PRES CENTERED N OF AREA NEAR 
36N136W EXTENDS A RIDGE SE ACROSS THE N WATERS TO NEAR 25N120W. 
MODERATE TO FRESH TRADE WINDS ARE BLOWING ON THE SOUTHERN 
PERIPHERY OF THE RIDGE. A STATIONARY FRONT CROSSES NW OF THE 
FORECAST REGION. LONG PERIOD NW SWELL GENERATED BEHIND THE FRONT 
ARE ALREADY IMPACTING THE NW WATERS...BUILDING SEAS TO AROUND 11 
FT NW OF LINE FROM 30N130W TO 19N140. THIS SWELL EVENT WILL 
CONTINUE TO PROPAGATE SE ACROSS THE REGIONAL WATERS DURING THE 
NEXT COUPLE OF DAYS...MERGING WITH A BROAD MIX OF SWELL 
ASSOCIATED WITH HURRICANE MIRIAM.   

GAP WINDS...A 1021 MB HIGH PRES LOCATED NEAR TAMPICO MEXICO  
CONTINUES TO SUPPORT NLY GAP WINDS THROUGH THE GULF OF 
TEHUANTEPEC. THE MOST RECENT ASCAT PASS PROVIDED OBSERVATIONS OF 
N TO NE WINDS IN THE 20-25 KT RANGE. MARINE GUIDANCE SUGGESTS 
THAT THESE WIND SPEEDS WILL CONTINUE THROUGH AND DOWNWIND OF THE 
GULF DURING THE NEXT 24 HOURS...WITH SEAS BUILDING TO 9 FT EARLY 
THIS MORNING. EXPECT WINDS TO DIMINISH BELOW 20 KT IN ABOUT 36 
HOURS AS HIGH PRES WEAKENS. 

$$
GR