000
AXPZ20 KNHC 200304
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC TUE SEP 20 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 
0245 UTC.

...SPECIAL FEATURE...

BROAD LOW PRES IS ANALYZED AS A 1009 MB SURFACE LOW PRES CENTER 
AT 13N95W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS 
OBSERVED N OF 10N BETWEEN 90W AND 100W WITH THE STRONGEST CELLS 
OVER THE EASTERN GULF OF TEHUANTEPEC. THIS LOW IS EXPECTED TO 
DRIFT W OVER THE NEXT COUPLE OF DAYS THROUGH AN AREA FAVORABLE 
FOR CONTINUED STRENGTHENING AND POSSIBLE TROPICAL CYCLONE 
FORMATION.
 
...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS NW ACROSS COSTA RICA AND ALONG 
THE PACIFIC COAST OF CENTRAL AMERICA TO EL SALVADOR THEN TURNS W 
INTO THE LOW PRES AT 13N95W. THE MONSOON TROUGH RESUMES OVER THE 
PACIFIC AT 17N115W TO LOW PRES AT 13.5N125W...CONTINUING SW TO 
THE LOW PRES AT 11N134W...THEN W TO BEYOND 10N140W. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION NOTED WITHIN 30 NM OF 
CENTRAL AMERICAN COAST FROM 83W TO 86W...AND N OF 10N BETWEEN 
90W AND 100W...AND WITHIN 60 NM EITHER SIDE OF A LINE FROM 
09N94W TO 07N101W TO 11N110W. 

...DISCUSSION... 

AN UPPER CYCLONE IS NEAR 32N139W WITH AN UPPER TROUGH SE TO NEAR 
24N132W. A SECOND UPPER TROUGH IS OVER NORTHERN OLD MEXICO TO 
THE N OF 23N ALONG 102W. AN UPPER RIDGE DISSECTS THE AREA 
THROUGH UPPER ANTICYCLONES AT 22N92W...23N110W...20N123W...AND 
19N141W. THE UPPER ANTICYCLONE AT 23N110W HAS A RIDGE EXTENDING 
NNW ACROSS SOUTHERN CALIFORNIA EFFECTIVELY SEPARATING THE TWO 
UPPER TROUGHS. THIS RESULTS IS VERY DRY ALOFT OVER THE AREA NW 
OF LINE FROM 10N140W TO 22N120W TO 22N106W. UPPER DIFFLUENCE 
ALONG THE SE PERIPHERY OF THE RIDGE IS ROUGHLY IN PHASE WITH THE 
LOWER LEVEL MONSOON TROUGH...AND ENHANCES CONVECTION AS 
PREVIOUSLY DESCRIBED. THE DEBRIS MOISTURE IS MOST DENSE NEAR 
13N125W AND IS ADVECTED SW TO THE EQUATOR AT 138W. AN UPPER 
TROUGH EXTENDS SW ACROSS THE NW CARIBBEAN TO A BASE OVER 
GUATEMALA LEAVING NORTHEASTERLY UPPER FLOW OVER THE DEEP TROPICS 
E OF 100W. 

MOISTURE FROM CONVECTION OVER CENTRAL AMERICA...AND OVER THE 
PACIFIC ALONG THE E SEGMENT OF THE MONSOON TROUGH...IS SPREADING 
SW TO ALONG 03N BETWEEN 80W AND 110W. 

AT THE LOW LEVELS A 1022 MB SURFACE HIGH IS AT 32N137W WITH A 
RIDGE AXIS SE TO 19N107W. AS PREVIOUSLY MENTIONED...THE MONSOON 
TROUGH AXIS EXTENDS FROM 17N116W TO 11N124W TO 10N140W. NE WINDS 
AT 20 KT...WITH COMBINED SEAS 6 TO 8 FT...ARE OBSERVED WITHIN 
120 NM N OF TROUGH AXIS BETWEEN 120W AND 140W. SOUTHWESTERLY 
WINDS AT 15 TO 20 KT...SEAS 7 TO 10 FT IN SW SWELL...ARE NOTED 
WITHIN ABOUT 480 NM SE OF THE TROUGH AXIS. THE TROUGH AXIS IS 
EXPECTED TO SHIFT SLIGHTLY W WITH THE GRADIENT RELAXING AND 
WINDS DIMINISHING BELOW 20 KT LATE TUE NIGHT.
 
GAP WINDS...NORTHERLY WINDS AT 20 TO 25 KT CONTINUE OVER THE 
WATERS N OF 14N BETWEEN 94.5W AND 96.5W...AND ARE EXPECTED TO 
CONTINUE THROUGH WED AS THE SURFACE LOW JUST TO THE S IS 
EXPECTED TO STRENGTHEN.
  
$$
NELSON