000
AXPZ20 KNHC 180301
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0245 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS W ACROSS COSTA RICA TO 09N86W TO 
15N95W THEN RESUMES OVER THE PACIFIC FROM 20N110W TO 12N120W TO 
10N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS 
OBSERVED WITHIN 120 NM EITHER SIDE OF A LINE FROM 05N78W TO 
12N97W TO 07N105W. SIMILAR CONVECTION IS NOTED WITHIN 120 NM 
EITHER SIDE OF A LINE FROM 22N108W TO 11N120W TO 10N140W.

...DISCUSSION... 

AN UPPER TROUGH IS N OF 27N ALONG 109W. A SECOND UPPER TROUGH 
EXTENDS ACROSS THE AREA THROUGH SMALL UPPER CYCLONES AT 33N131W 
AND 28N129W AND 24N136W AND 19N135W WITH THE TROUGH CONTINUING 
SW TO A BASE AT 14N141W. A SMALL UPPER ANTICYCLONE IS 
IMMEDIATELY W AT 31N141W WITH AN UPPER RIDGE EXTENDING SE TO A 
SHARP CREST AT 28N134W. UPPER MOISTURE REMAINS N OF 32N...WITH 
VERY DRY UPPER AIR SUGGESTED W OF A LINE FROM 30N103W TO 12N140W.

AN UPPER ANTICYCLONE IS OVER CENTRAL OLD MEXICO AT 22N104W WITH 
A RIDGE EXTENDING SW OVER THE TROPICAL PACIFIC TO A CREST AT 
11N134W. UPPER DIFFLUENCE ALONG THIS RIDGE IS ENHANCING THE 
PREVIOUSLY DESCRIBED CONVECTION ALONG THE AXIS OF THE MONSOON 
TROUGH. SOME OF THE DEBRIS MOISTURE IS ADVECTED N AND NE ACROSS 
THE UPPER RIDGE ACROSS CENTRAL OLD MEXICO FROM 20N TO 26N. 

AN UPPER TROUGH ALSO DOMINATES THE E COAST OF N AMERICA... 
CONTINUING SW ACROSS THE FLORIDA STRAITS THROUGH AN UPPER 
CYCLONE OVER BELIZE AT 16N88W...TO ANOTHER OVER THE PACIFIC AT 
06N94W. AN UPPER ANTICYCLONE IS OVER THE W CARIBBEAN AT 16N82W 
WITH ITS ENVELOPE OF ANTICYCLONIC FLOW EXTENDING S OVER THE 
TROPICS BETWEEN 75W AND 90W. A LOW LEVEL TROUGH IS MOVING W 
ACROSS HONDURAS UNDER THE ASSOCIATED UPPER RIDGE RESULTING IN 
CONSIDERABLE CONVECTION OVERLAND. DEBRIS MOISTURE FROM THIS 
CONVECTION OVER CENTRAL AMERICA...AND OVER THE PACIFIC S OF THE 
MONSOON TROUGH...IS SPREADING SW TO ALONG THE EQUATOR E OF 88W 
AND TO ALONG 03N BETWEEN 88W AND 110W.

AT THE LOW LEVELS...1025 MB HIGH PRESSURE IS CENTERED NW OF THE 
AREA AT 35N136W WITH A RIDGE EXTENDING SE TO 15N115W. AS 
PREVIOUSLY MENTIONED THE MONSOON TROUGH AXIS EXTENDS FROM 
18N110W TO 11N125W TO LOW PRES 1010 MB AT 11N134W TO 10N140W. NE 
WINDS AT 20 KT...SEAS 6 TO 8 FT...ARE OBSERVED WITHIN 240 NM N 
OF TROUGH AXIS BETWEEN 128W AND 140W. SOUTHWESTERLY WINDS AT 15 
TO 20 KT...SEAS 6 TO 8 FT...ARE NOTED FROM 06N TO TROUGH AXIS 
BETWEEN 107W AND 140W. THE TROUGH AXIS IS EXPECTED TO SHIFT 
SLIGHTLY W WITH THE AREA OF SOUTHWESTERLY WINDS EXPANDING OUT TO 
ABOUT 480 NM SE OF THE TROUGH AXIS BY LATE MON.
 
GAP WINDS...NORTHERLY WINDS AT 15 TO 20 KT CONTINUE OVER THE 
WATERS N OF 14N BETWEEN 94W AND 96W...AND ARE EXPECTED TO 
INCREASE TO 20 TO 25 KT SUN THROUGH MON.
  
$$
NELSON