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ENSO Quick Look IRI ENSO Update / Prediction Technical ENSO Update IRI Probabilistic ENSO Prediction ENSO Prediction Plume Monthly archive ENSO Update20 October 2011SummaryThe ending of a moderate to strong La Niña episode in early May 2011 was followed by neutral ENSO conditions until early August, when weak La Niña conditions returned and have been gradually strengthening. For the October-December season currently in progress, there is an approximately 78% probability for continuing La Niña conditions, a 22% probability for returning to neutral conditions, and virtually no chance for the development of El Niño conditions. Weak to moderate La Niña conditions are the most likely scenario for the remainder of 2011, into the first couple of months of 2012.General Discussion
In mid-October 2011, the NINO3.4 SST anomaly index was at -0.8 C away from average,
indicative of weak La Niña conditions. Sea temperatures below the ocean surface
have been increasingly below average between August and mid-October. Zonal
wind anomalies in the equatorial Pacific feature a somewhat enhanced strength of
easterlies, and the Southern Oscillation Index is at slightly above average levels,
at a borderline to weak La Niña level. These observations indicate that the ENSO condition
continues to be that of weak La Niña, as has been the case since early August.
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