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ENSO Update

20 January 2011

Summary

Moderate to strong La Niña conditions have been observed since mid-August 2010, and continue as of mid-January 2011. For the January-March season currently in progress, there is an approximate 98% probability for continuing La Niña conditions, and a 2% probability for returning to neutral ENSO conditions. Probabilities for La Niña conditions continue at 88% for the February-April season, and do not drop to below 50% until the April-June season.

General Discussion

In mid-January, the NINO3.4 SST anomaly index continues at values indicative of moderate to strong La Niña levels (1.7 degrees C below average). Zonal wind anomalies in the equatorial Pacific continue to feature markedly stronger than average easterlies, and subsurface oceanic heat content continues to be well below average. These observations indicate a high probability of the continuation of La Niña conditions for at least another two to four months.

Out of a large set of dynamical and statistical prediction models, 100% of them indicate maintenance of La Niña conditions during the upcoming February-April 2011 season. Overall, based on model predictions and current observations of the ocean surface and subsurface, for the February-April and the March-May seasons the probability for La Niña conditions is approximately 88% and 67%, respectively. By the April-June season the probability for La Niña conditions is estimated at approximately 46%, decreasing to less than 30% for June-August and beyond. Probabilities for El Niño conditions are 10% or less through April-June, rising to the 20%-25% range from the June-August season onward.

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