000
AXPZ20 KNHC 202146
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2145 UTC.

...SPECIAL FEATURE...

A 1008 MB LOW PRES EMBEDDED WITHIN THE MONSOON TROUGH ABOUT 150 
NM SSE OF PUERTO ESCONDIDO MEXICO NEAR 13.5N96W HAS A BROAD AREA 
OF ACTIVE AND INCREASINGLY ORGANIZING DEEP CONVECTION. THE 
CIRCULATION CENTER SHOWS UP WELL IN VISIBLE SATELLITE IMAGERY.
A 1238 UTC WINDSAT PASS DEPICTED THE BROAD CIRCULATION BUT 
EXTENSIVE CONVECTIVE ACTIVITY RESULTED IN NUMEROUS RAIN FLAGGED 
VECTORS WHICH MASKED THE INNER STRUCTURE OF THE LOW. THE LOW IS 
SITUATED BENEATH AN UPPER LEVEL ANTICYCLONE INDICATING FAVORABLE 
CONDITIONS FOR ADDITIONAL DEVELOPMENT. THERE IS A HIGH 
PROBABILITY OF TROPICAL CYCLONE FORMATION IN THE NEXT 48 HOURS. 
OF NOTE...IT HAS BEEN 30 DAYS SINCE THE LAST NAMED TROPICAL 
CYCLONE...TROPICAL STORM GREG...OCCURRED IN THE EAST PACIFIC 
BASIN. THIS IS ONE OF THE LONGEST STRETCHES BETWEEN TROPICAL 
CYCLONE OCCURRENCES IN THE PEAK OF THE HURRICANE SEASON. 
 
...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH AXIS EXTENDS FROM 09N80W TO 1008 MB LOW NEAR 
14N96W TO 09N106W TO 15N114W TO 1011 MN LOW NEAR 12N121W TO 
13N127W TO 1011 MB LOW NEAR 11N136W TO 10N140W. SCATTERED 
MODERATE CONVECTION IS FROM 05N TO 08N BETWEEN 78W AND 87W. 
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS FROM 09N TO 
16N BETWEEN 90W AND 102W. SCATTERED MODERATE CONVECTION IS FROM 
08N TO 14N BETWEEN 110W AND 114W.    

SCATTERED MODERATE ISOLATED STRONG CONVECTION N OF 07N TO TROUGH 
AXIS BETWEEN 82W AND 87W AND FROM 09N TO THE MONSOON TROUGH 
BETWEEN 90W AND 103W. 

SCATTERED MODERATE ISOLATED STRONG CONVECTION FROM 08N TO 13N 
BETWEEN 110W AND 113W. 

...DISCUSSION... 

1022 MB HIGH PRES CENTERED NEAR 32N139W CONTINUES TO WEAKEN 
AHEAD OF A DEEP LAYER TROUGH DIGGING EASTWARD FROM THE N CENTRAL 
PACIFIC. A WEAK RIDGE EXTENDS E-SE FROM THE HIGH TO NORTHERN 
BAJA CALIFORNIA. SCATTEROMETER DATA SHOWS GENERALLY LIGHT TO 
MODERATE TRADE WIND FLOW N OF 15N AND S OF THE SURFACE RIDGE. 
WINDS ARE NE AT 15 KT CLOSER TO THE MONSOON TROUGH...WITH LIGHT 
S TO SW FLOW S OF THE TROUGH AXIS. TWO WEAK LOWS EMBEDDED WITHIN 
THE MONSOON TROUGH ARE LOCATED NEAR 11N121W AND 11N136W. BOTH 
ARE 1011 MB AND BOTH LACK SIGNIFICANT DEEP CONVECTION. WEAK 
LOW-LEVEL CONVERGENCE AND A LACK OF DEEP LAYERED MOISTURE IS 
SUPPRESSING CONVECTION ASSOCIATED WITH THE MONSOON TROUGH W OF 
118W. NW SWELL REACHING AS HIGH AS 12 FT WITH PERIODS TO 17 
SECONDS WILL PUSH INTO THE NW PORTION OF THE DISCUSSION AREA BY 
WED AFTERNOON AND CONTINUE INTO THU. 

AN UPPER RIDGE EXTENDS E-W ALONG 20N THROUGH CENTRAL MEXICO. A 
BREAK IN THE RIDGE IS EVIDENT ALONG 95W...PROVIDING A FAVORABLE 
LOW SHEAR ENVIRONMENT FOR THE DEVELOPING LOW PRES NEAR 13.5N96W.
REFER TO SPECIAL FEATURES SECTION ABOVE FOR ADDITIONAL 
INFORMATION. MODERATE S TO SW FLOW IS EXPECTED TO INCREASE THIS 
EVENING AND TONIGHT AFTERNOON AS THE LOW DEEPENS...ALLOWING SEAS 
TO BUILD TO 8 TO 10 FT S OF THE LOW FROM 04N TO 11N BETWEEN 95W 
AND 105W. THE DEEPENING LOW WILL ALSO ENHANCE N TO NE GAP WINDS 
FLOWING THROUGH THE GULF OF TEHUANTEPEC...ALTHOUGH THIS WILL 
VEER MORE TOP THE E AND TAPER OFF THROUGH LATE WED AS THE LOW 
TRACKS FURTHER W...ALLOWING MORE SOUTHERLY FLOW TO PREVAIL 
THROUGH THE GULF OF TEHUANTEPEC.
  
$$
COBB