000
AXPZ20 KNHC 180919
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN SEP 18 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0845 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS W ACROSS PANAMA TO 08N82W TO 
10N90W TO 09N95W THEN BREAKING AT 12N100W. THE TROUGH RESUMES 
FROM 20N110W TO 15N110W TO 09N140W. SCATTERED MODERATE ISOLATED 
STRONG CONVECTION IS OBSERVED WITHIN 120 NM OF THE COAST BETWEEN 
12N AND 16N. SCATTERED MODERATE CONVECTION WITHIN 60 NM EITHER 
SIDE OF MONSOON TROUGH BETWEEN 115W AND 135W.

...DISCUSSION... 

N OF 20N...A LOW AMPLITUDE MID TO UPPER LEVEL RIDGE IS MIGRATING 
EASTWARD N OF THE AREA THROUGH ROUGHLY 130W. A RELATED SURFACE 
RIDGE EXTENDS FROM 1026 MB HIGH PRES THROUGH THE SOUTHERN BAJA 
PENINSULA. SCATTEROMETER PASSES OVER THE PAST SEVERAL HOURS 
INDICATE GENERALLY LIGHT TO MODERATE NE SURFACE WINDS...WITH THE 
EXCEPTION OF OFF THE COAST OF BAJA WHERE 15 TO 20 KT WINDS WERE 
REPORTED BY SEVERAL SHIPS IN THE PAST HOUR. THIS ENHANCED FLOW 
IS DUE TO THE SURFACE RIDGE BUILDING EASTWARD WITH THE UPPER 
RIDGE...TIGHTENING THE GRADIENT AGAINST TROUGHING OVER N CENTRAL 
MEXICO AND TERRAIN OVER BAJA. 

S OF 20N W OF 120W...A SURFACE RIDGE N OF THE AREA IS 
MAINTAINING 15 TO 20 KT TRADE WINDS BETWEEN THE MONSOON TROUGH 
AXIS TO AROUND 15N...AS OBSERVED BY A WINDSAT PASS AT 0230 UTC 
AND AN EARLIER ASCAT PASS AT 1830 UTC. THE WINDSAT PASS ALSO 
INDICATED 20 KT S TO SW FLOW TO THE SOUTH OF THE MONSOON TROUGH 
BETWEEN ROUGHLY 125W AND 135W. THE CONVERGENT FLOW IS RESULTING 
IN SCATTERED MODERATE SHOWERS AND TSTMS IN THIS AREA AS WELL 
ALONG THE MONSOON TROUGH. 

S OF 20N E OF 120W...AN ASCAT PASS FROM AROUND 0400 UTC SHOWS 
AND PERSISTENT ELONGATED CYCLONIC CENTER ALONG THE MONSOON 
TROUGH AXIS BETWEEN ROUGHLY 105W AND 115W. WHILE NO DISTINCT LOW 
CENTER AS EMERGED...GLOBAL MODELS CONTINUE TO SHOW A WEAK LOW 
PRES AREA DEVELOPING OVER THE NEXT COUPLE OF DAYS IN THIS AREA 
AND DRIFTING W ALONG THE MONSOON TROUGH AXIS. THE MAIN IMPACT OF 
THIS WILL BE SW WINDS REACHING 20 KT WITHIN 180 NM ON THE SOUTH 
SIDE OF THE MONSOON TROUGH MAINLY BETWEEN 110W AND 130W OVER THE 
NEXT SEVERAL DAYS...WITH SEAS TO 9 FT. GIVEN THAT GLOBAL MODELS 
HAVE BEEN ADVERTISING THIS FEATURE FOR THE PAST COUPLE 
NIGHTS...BUT THAT IT HAS NOT YET FULLY DEVELOPED...WILL GO BELOW 
GUIDANCE ON DEVELOPMENT OF WINDS AND SEAS IN THE FORECAST. THE 
MONSOON TROUGH BREAKS HERE...BUT PICKS UP FURTHER TO THE SE 
WHERE ANOTHER WEAK LOW IS STARTING TO SLOWLY DEVELOP NEAR 10N93W 
WHERE LIGHT NW FLOW AT TOGA-TAO BUOY 43301 COMPLIMENTS WELL 
DEFINED CYCLONIC TURNING JUST TO THE EAST PER THE 0400 UTC ASCAT 
PASS. SW WINDS WILL INCREASE THROUGH TONIGHT ON THE S SIDE OF 
THE LOW AS IT DEVELOPS AND DRIFTS W ALONG THE MONSOON TROUGH 
AXIS. FURTHER NORTH...WINDS HAVE APPROACHED 20 KT THROUGH THE 
TEHUANTEPEC AREA PER REPORTS FROM SALINA CRUZ ON THE PACIFIC 
COAST. THE 0400 UTC ASCAT PASS ALSO SHOWED 15 KT IN THIS AREA. 
THIS IS A LITTLE LESS THAN EXPECTED...BUT GIVEN THE DEVELOPMENT 
OF WEAK LOW PRES TO THE SOUTH...EXPECT 20 KT FLOW THROUGH 
TEHUANTEPEC THROUGH MON...WITH DIURNAL MAXIMUMS IN THE EARLY 
MORNING.
  
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CHRISTENSEN