Tropical Highlights � September 2011

 

 

La Ni�a 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 Ni�o indices were -0.7�C for the Ni�o 3.4 region and -0.6�C for the Ni�o 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 Ni�a 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