000
AXPZ20 KNHC 212151
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI SEP 21 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...
SURFACE LOW PRES 1006 MB EMBEDDED IN MONSOON TROUGH AT 14N105W 
EXPECTED TO DRIFT W-NW AND INTENSIFY REACHING 15N108W SAT AND 
16N111W SUN.  SCATTERED MODERATE TO STRONG CONVECTION FROM 
10-15N BETWEEN 105W-110W AND GETTING BETTER ORGANIZED.  TROPICAL 
CYCLONE FORMATION EXPECTED WITHIN NEXT 24-36 HOURS.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH FROM 09N94W TO 13N102W TO 1006 MB LOW PRES AT 
14N105W TO 10N127W THEN ITCZ TO 11N133W TO BEYOND 07N140W. 
SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 240 NM S OF 
AXIS E OF 87W AND FROM 93W TO 111W.  SCATTERED MODERATE TO 
STRONG CONVECTION WITHIN 180 NM NW QUADRANT OF LOW PRES CENTER 
AT 14N105W.  SCATTERED MODERATE CONVECTION WITHIN 120 NM S OF 
AXIS W OF 129W.
 
...DISCUSSION...
BROAD ANTICYCLONE AT 11N139W FORCED S BY APPROACHING UPPER LEVEL 
TROUGH CURRENTLY EXTENDING FROM 32N133W TO BEYOND 28N140W.    
ABUNDANT TROPICAL MOISTURE RIDES 70 KT JET CORE AHEAD OF TROUGH 
AXIS.  RIDGE CREST TILTS NE TRAPPED BETWEEN THAT TROUGH AND A 
SECOND ONE ANCHORED BY CYCLONE ALOFT AT 01N124W AND A SECOND ONE 
AT 16N124W.  EASTERNMOST TROUGH THEN EXTEND NE TO 25N112W.  
EXCEPT ABOVE MENTIONED MOISTURE SWATH...MOST OF BASIN N OF 10N W 
OF 118W REMAINS VERY DRY AND STABLE.  NEXT UPPER FEATURE IS 
ANTICYCLONE AT 14N99W...STACKED ABOVE SURFACE LOW PRES 1006 MB 
AT 14N105W...PROVIDING LIGHT WIND SHEAR ENVIRONMENT AND 
ENHANCING OUTFLOW.  SEE SPECIAL FEATURES ABOVE FOR LOW PRES 
DETAILS.

...ELSEWHERE AT LOWER LEVELS...
SURFACE HIGH PRES CENTER 1026 MB N OF BASIN BRINGS MODERATE TO 
FRESH N BREEZE ACROSS 30N BETWEEN 121W AND 126W BUILDING SEAS TO 
9 FT THROUGH SAT.  WIND AND SEAS SUBSIDE LATE SAT.  PRES 
GRADIENT BETWEEN RIDGE AND ITCZ PROMPTS SURGE OF FRESH NE BREEZE 
W OF 135W FROM 10N TO 15N EXPECTED TO DIMINISH LATE SAT. 

SWATH OF STRONG NE WINDS OVER GULF OF TEHUANTEPEC EXPECTED TO 
REMAIN WITH LITTLE CHANGE THROUGH SUN.

$$
WALLY BARNES