000
AXPZ20 KNHC 161005
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN OCT 16 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 
1015 UTC.

...SPECIAL FEATURES...

THE CENTER OF TROPICAL DEPRESSION AT 16/0900 UTC IS NEAR 14.3N 
107.5W. IRWIN IS MOVING SOUTH-SOUTHWESTWARD OR 210 DEGREES
04 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. THE
MAXIMUM SUSTAINED WIND SPEEDS ARE 30 KT WITH GUSTS TO 40 KT.
SCATTERED STRONG RAINSHOWERS ARE WITHIN 90 NM IN THE SOUTHERN 
QUADRANT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO 
HEADERS MIATCMEP1/WTPZ21 KNHC FOR MORE DETAILS. 
 
...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH HAS BEEN DISRUPTED IN THE EASTERN PACIFIC 
OCEAN BETWEEN MEXICO AND CENTRAL AMERICA AND TROPICAL DEPRESSION 
IRWIN. THE MONSOON TROUGH EXTENDS 12N112W TO 09N124W TO 11N140W. 
SCATTERED STRONG RAINSHOWERS ARE FROM 13N TO 14N BETWEEN 90W AND 
96W. SCATTERED MODERATE RAINSHOWERS ARE WITHIN A 60 NM RADIUS OF
9N115W...FROM 06N TO 08N BETWEEN 120W AND 127W...AND FROM 08N TO 
09N BETWEEN 133W AND 136W. ISOLATED MODERATE RAINSHOWERS ARE FROM
9N TO 12N BETWEEN 139W AND 140W.

...DISCUSSION...

AN UPPER LEVEL CYCLONIC CIRCULATION CENTER IS NEAR 31N137W.
UPPER LEVEL CYCLONIC WIND FLOW COVERS THE AREA TO THE WEST OF 
THE LINE THAT PASSES THROUGH 32N125W TO 23N131W BEYOND 16N140W.
A 1007 MB LOW PRESSURE CENTER 31N137W. THIS LOW CENTER IS 
FORECAST TO MOVE SOUTHEASTWARD DURING THE FIRST 24 HOURS OF THE 
FORECAST PERIOD...AND THEN MOVE NORTHWARD AND WEAKEN BY 48 HOURS 
AT THE END OF THE FORECAST PERIOD. A COLD FRONT EXTENDS FROM THE
LOW CENTER...PASSING THROUGH 32N131W TO 27N132W BEYOND 20N140W.



A 1006 MB LOW PRES IS SPINNING JUST N OF THE AREA NEAR 31N138W. 
A COLD FRONT EXTENDS FROM THE LOW TO 30N131W TO 21N140W. LATEST 
SCATTEROMETER DATA AS WELL AS A SHIP OBSERVATIONS INDICATE FRESH 
TO STRONG W TO NW WINDS IN THE WAKE OF THE FRONT. SEAS ARE ALSO 
RUNNING UP TO 14 FT IN NW SWELL OVER THE NW PART OF THE AREA 
BEHIND THE FRONTAL SYSTEM. THE LOW PRESSURE AREA WILL SLOWLY 
SHIFT E OVER THE NEXT 48 HOURS...AND REMAIN ALONG OR JUST N OF 
30N. THE FRONT WILL SHIFT SLOWLY E THEN DISSIPATE WITHIN 48 
HOURS WITH ASSOCIATED WINDS DIMINISHING BELOW 20 KT. THE NW 
SWELL WILL CONTINUE TO PROPAGATE S AND SE THROUGH THE FORECAST 
PERIOD WITH COMBINED SEAS GRADUALLY SUBSIDING TO NEAR 9 FT. 

AN EXTENSIVE AREA OF FRESH TO STRONG SW MONSOONAL FLOW PREVAILS 
N OF 06N E OF 100W. THIS MONSOONAL FLOW CONTINUES TO ADVECT 
ABUNDANT MOISTURE NORTHWARD INTO PARTS OF CENTRAL AMERICA AND 
S MEXICO WHICH WILL BRING PERIODS OF VERY HEAVY RAINFALL OVER 
PORTIONS OF THE PACIFIC COASTS OF SOUTHEASTERN MEXICO... 
GUATEMALA...EL SALVADOR...SOUTHERN HONDURAS AND NICARAGUA. THESE 
PERIODS OF HEAVY MONSOONAL RAINFALL HAS THE POTENTIAL TO CREATE 
LIFE-THREATENING FLASH FLOODS AND MUD SLIDES OVER THESE AREAS.

AN EARLIER HIGH RESOLUTION ASCAT PASS INDICATED 20-30 KT 
NORTHERLY WINDS IN AND DOWNSTREAM OF THE GULF OF TEHUANTEPEC 
AROUND A BROAD CYCLONIC CIRCULATION CURRENTLY CENTERED OVER THE 
YUCATAN PENINSULA NEAR 19N88W. DUE TO THE INFLUENCE OF THIS 
CYCLONIC CIRCULATION OVER THE AREA...THE WINDS FUNNELING INTO 
THE GULF OF TEHUANTEPEC ARE TURNING NW THEN WEST AS IT MOVES 
FURTHER FROM THE GULF OF TEHUANTEPEC. TYPICALLY...THE WINDS 
BLOWING THROUGH THE CHIVELA PASS INTO THE GULF OF TEHUANTEPEC 
TURN NE THEN E AS IT MOVES FURTHER FROM THIS GULF. THIS 
WEATHER PATTERN IS FORECAST TO PERSIST OVER THE NEXT COUPLE OF 
DAYS AS THE BROAD LOW PRESSURE AREA MOVES W-NW PROBABLY TOWARD 
THE BAY OF CAMPECHE. 

THE REMAINDER OF THE REGIONAL WATERS E OF 130W ARE DOMINATED BY 
MERGING NW AND SW SWELL. THIS SWELL EVENT WILL GRADUALLY SUBSIDE 
FROM THE NW TO SE THROUGH THE NEXT 48 HOURS...WITH SEAS GREATER 
THAN 8 FT LIMITED TO S OF 12N AND E OF 125W BY MON. 

$$
MT