000
AXPZ20 KNHC 111550
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SUN SEP 11 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1500 UTC.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH EXTENDS FROM SW CARIBBEAN ACROSS NORTHERN COSTA 
RICA...ENTERING THE EPAC WATERS NEAR 10N86W TO 21N110W TO A 1008 
MB LOW NEAR 16N117W TO A 1009 MB LOW PRES NEAR 13N132W TO 
10N140W. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS N 
OF 06N AND S OF THE MONSOON TROUGH BETWEEN 80W AND 94W. SIMILAR 
CONVECTION IS FROM 7N TO 10N BETWEEN 99W AND 104W. SMALL CLUSTER 
OF MODERATE TO STRONG CONVECTION WITHIN 50 NM OF 21.5N112.5W.

...DISCUSSION...
A RIDGE/TROUGH/RIDGE PATTERN DOMINATES MOST OF THE FORECAST 
REGION. AN UPPER ANTICYCLONE IS CENTERED W OF THE AREA WITH A 
RIDGE EXTENDING NE OVER THE NW CORNER OF THE FORECAST REGION AND 
WELL BEYOND 36N135W. ANOTHER UPPER ANTICYCLONE IS OVER SW MEXICO 
AT 21N105W WITH AN UPPER RIDGE EXTENDING W OVER THE PACIFIC TO 
NEAR 17N130W...AND RIDGING N-NW INTO NEW MEXICO. BETWEEN 
RIDGES...THERE IS AN UPPER LEVEL TROUGH WITH AXIS EXTENDING FROM 
AN UPPER LEVEL LOW OVER SOUTHERN CALIFORNIA TO ANOTHER WEAK LOW 
NEAR 18N135W. UPPER LEVEL NE TO E FLOW DOMINATES THE DEEP 
TROPICS TO THE S OF THESE FEATURES. 

AT THE SURFACE...A WEAK HIGH PRES RIDGE CONTINUES OVER THE N 
WATERS YIELDING NE TRADES AT LESS THAN 20 KT. THE MONSOONAL FLOW 
ALSO REMAINS WEAK WITH WINDS BELOW 20 KT. AS TROPICAL CYCLONE 
NATE SHIFTS W OVER THE NEXT 24 HOURS NLY WINDS TO 20 KT WILL 
BEGIN TO AFFECT THE GULF OF TEHUANTEPEC BY TONIGHT.

SHOWER ACTIVITY REMAINS MINIMAL IN ASSOCIATION WITH THE AREA OF 
LOW PRESSURE CENTERED NEAR 16N117W OR ABOUT 650 MILES SOUTHWEST 
OF THE SOUTHERN TIP OF BAJA CALIFORNIA. DEVELOPMENT OF THIS 
SYSTEM APPEARS UNLIKELY DUE TO UNFAVORABLE UPPER-LEVEL WINDS AND 
COOLER WATER ALONG THE EXPECTED TRACK. THIS SYSTEM HAS A LOW 
CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS 
AS IT MOVES SLOWLY NORTHWARD. AN EARLIER ASCAT SHOWED THE 
CYCLONIC CIRCULATION ASSOCIATED WITH THIS SYSTEM WITH WINDS IN 
THE 10 TO 15 KT RANGE.  

THE SMALL AREA OF LOW PRESSURE LOCATED NEAR 13N132W OR ABOUT 
1650 MILES WEST-SOUTHWEST OF THE SOUTHERN TIP OF BAJA CALIFORNIA 
CONTINUES TO PRODUCE DISORGANIZED SHOWERS AND THUNDERSTORMS. 
DEVELOPMENT...IF ANY...SHOULD BE SLOW TO OCCUR AS THE LOW BEGINS 
TO MOVE SLOWLY WESTWARD OR WEST-SOUTHWESTWARD. THIS SYSTEM HAS 
ALSO A LOW CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 
48 HOURS.

NORTHERLY SWELLS...RESULTING IN COMBINED SEAS OF 9 FT... 
PREVAILS OVER THE WATERS N OF 25N BETWEEN 118W AND 135W. THIS 
SWELL EVENT WILL SPREAD SLIGHTLY FURTHER S BEFORE SUBSIDING 
BELOW 8 FT MON NIGHT. CROSS EQUATORIAL SW SWELL...WITH SEAS TO 9 
FT...WILL MOVE N OVER THE WATERS S OF 10N W OF 90W. THIS SWELL 
WILL CONTINUE TO SPREAD NORTHWARD THROUGH THE FORECAST PERIOD 
REACHING THE COAST OF MEXICO S OF SOUTHERN BAJA CALIFORNIA THIS 
MON.

$$
GR