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ENSO Quick Look IRI ENSO Update / Prediction Technical ENSO Update IRI Probabilistic ENSO Prediction ENSO Prediction Plume Monthly archive ENSO Update15 September 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. For the September-November season currently in progress, there is an approximately 52% probability for continuing La Niña conditions, a 48% probability for returning to neutral conditions, and virtually no chance for the development of El Niño conditions. Although weak La Niña conditions are the most likely scenario for the remainder of 2011, a return to neutral conditions is also possible.General Discussion
In mid-September 2011, the NINO3.4 SST anomaly index was at -0.7 C away from average,
indicative of weak La Niña conditions. Sea temperatures below the ocean surface
also became somewhat below average during August and so far in September. Zonal
wind anomalies in the equatorial Pacific feature a slightly enhanced strength of
easterlies, and the Southern Oscillation Index is at slightly above average levels,
although still in a neutral range. These observations indicate that the ENSO condition
has moved from cool-neutral to weak La Niña between early August and mid-September.
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