Tropical Highlights – September 2011

 

 

La Niña conditions strengthened during September 2011 as sea surface temperature anomalies were below -0.5°C across much of the eastern and central equatorial Pacific Ocean (Fig. T18, Table T2). The latest monthly Niño indices were -0.7°C for the Niño 3.4 region and -0.6°C for the Niño 1+2 region (Table T2, Fig. T5). Consistent with these conditions, the oceanic thermocline (measured by the depth of the 20°C isotherm) remained shallower than average in the east-central equatorial Pacific (Figs. T15 and T16), where corresponding sub-surface temperatures were 1-3°C below average (Fig. T17).

Also in September, the equatorial low-level easterly trade winds and upper-level westerly winds remained stronger than average over the central equatorial Pacific (Table T1, Figs. T20 and T21).  Convection remained enhanced over western equatorial Pacific and suppressed near the Date Line and south of the Equator (Figs. T25 and E3). Collectively, these oceanic and atmospheric anomalies reflect a strengthening of La Niña conditions that developed during August.

 

 

For the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html