000
AXPZ20 KNHC 120251
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC MON SEP 12 2011

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0200 UTC.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH EXTENDS FROM EXTREME SOUTHWEST CARIBBEAN WNW 
ACROSS N PORTIONS OF COSTA RICA AND ENTERS EPAC WATERS NEAR 
10N86W TO 09N90W TO 10N99W TO 22N110W TO 1008 MB LOW PRES AT 
17N116.5W TO 1009 MB LOW PRES AT 12N144W THEN TRANSITIONS TO 
ITCZ TO BEYOND 10N140W. SCATTERED MODERATE TO STRONG CONVECTION 
NOTED WITH 60 NM N AND 270 NM S OF AXIS BETWEEN 83W AND 108W. 
NUMEROUS MODERATE TO STRONG WITHIN 120 NM OF COASTLINE FROM 86W 
TO 92W. 

...DISCUSSION...
A RIDGE/TROUGH/RIDGE PATTERN DOMINATES MOST OF THE FORECAST AREA 
N OF 10N THIS EVENING. AN UPPER ANTICYCLONE IS CENTERED JUST W 
OF THE AREA NEAR 26N142W WITH A RIDGE EXTENDING NE TO NEAR 
30N140W THEN SHARPLY NNE TO BEYOND 40N133W. ANOTHER UPPER 
ANTICYCLONE IS OVER C CENTRAL MEXICO NEAR 23N104W WITH AN UPPER 
RIDGE EXTENDING WSW OVER THE PACIFIC TO NEAR 18N130W...AND 
RIDGING TO THE N OVER TEXAS AND NEW MEXICO. BETWEEN RIDGES... A 
COMPLEX CUTOFF UPPER LEVEL CYCLONE WAS CENTERED NEAR 39N120W 
WITH UPPER LEVEL TROUGH AXIS EXTENDING SSW THROUGH 29N123W THEN 
MEANDERS SW TO A MIDDLE TO UPPER CYCLONE 17N138W. THE WESTERN 
MOST RIDGE IS FORECAST TO BECOME NARROW AND SHIFT SLIGHTLY W 
OVER THE NEXT FEW DAYS WHILE THE EASTERN MOST RIDGE EXPANDS WWD 
AND BECOMES THE DOMINANT FEATURE. TO THE S OF THESE FEATURES... 
UPPER LEVEL NE TO E FLOW DOMINATES THE DEEP TROPICS TO 130W. 

AT THE SURFACE...A WEAK HIGH PRES RIDGE CONTINUES OVER THE NW 
WATERS PRODUCING MAINLY LIGHT TO MODERATE NE TRADEWINDS W OF 
126W. THE MONSOONAL FLOW ALSO REMAINS MILD WITH WINDS BELOW 20 
KT....BUT HAD BACKED S TO SW ACROSS THE AREA E OF 115W 
TODAY...AIDING IN FORCING AN ELONGATED ZONE OF DEEP CONVECTION 
MAINLY S OF THE MONSOON TROUGH. NLY WINDS TO 20 KT ARE FORECAST 
TO BEGIN TO BLOW ACROSS THE GULF OF TEHUANTEPEC IN THE NEXT FEW 
HOURS AS THE REMNANTS TROPICAL CYCLONE NATE CONTINUES TO MOVE W 
AND FARTHER INLAND ACROSS CENTRAL MEXICO. GUIDANCE SUGGESTS 
WINDS WILL INCREASE ACROSS THE GULF OF TEHUANTEPEC TO 20 TO 25 
KT ON MONDAY.

A TROPICAL WAVE MOVING W ACROSS THE W CARIBBEAN WAS ENTERING 
CENTRAL AMERICA ACROSS NICARAGUA AND HONDURAS THIS 
EVENING...PRODUCING WIDESPREAD SHOWERS AND THUNDERSTORMS THERE. 
THIS WEATHER WILL SHIFT SLOWLY W ACROSS CENTRAL AMERICA AND 
ADJACENT PACIFIC WATERS IN THE NEXT 24 HOURS...PRODUCING AREAS 
OF VERY HEAVY RAINFALL.

THE PAIR OF LOW PRESSURE CENTERED EMBEDDED WITHIN THE MONSOON 
TROUGH MENTIONED ABOVE CONTINUE TO SLOWLY WEAKEN AND WILL BE 
DEVOID OF 20 KT WINDS WITHIN 20 HOURS. CONVECTION CONTINUES TO 
FLARE WITH THE WESTERN MOST LOW BUT IS LIKELY TO DIMINISH BY 24 
HOURS. 

NORTHERLY SWELLS...RESULTING IN COMBINED SEAS OF 8 FT... 
PREVAILS OVER THE WATERS N OF 27N BETWEEN 122W AND 135W. THIS IS 
THE MAXIMUM EXTENT THAT 8 FT SEAS ARE EXPECTED TO REACH WITH 
THIS EVENT AND WILL DIMINISH TO LESS THAN 8 FT WITHIN 24 HOURS.  
CROSS EQUATORIAL SW SWELL...WITH SEAS TO 9 FT...WILL MOVE N OVER 
THE WATERS S OF 10N W OF 90W. THIS SWELL EVENT WILL CONTINUE TO 
SPREAD NORTHWARD THROUGH THE FORECAST PERIOD REACHING THE COAST 
OF MEXICO S OF SOUTHERN BAJA CALIFORNIA DURING THE DAY.

$$
STRIPLING