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ENSO Update

16 December 2010

Summary

Moderate to strong La Niña conditions have been observed since mid-August 2010. For the December-February season currently in progress, there is an approximately 98% probability for continuing La Niña conditions, and a 2% probability for returning to neutral ENSO conditions. Probabilities for La Niña conditions continue at 94% or more through the January-February-March season of 2011, and do not drop to below 50% until the April-June season.

General Discussion

In mid-December, the NINO3.4 SST anomaly index continues at values indicative of moderate to strong La Niña levels (1.5 degrees C below average). Zonal wind anomalies in the equatorial Pacific continue to feature 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 January-March 2011 season. Overall, based on model predictions and current observations of the ocean surface and subsurface for the December-February and the January-March seasons, the probability for La Niña conditions is approximately 98% and 94%, respectively. By the March-May season the probability for La Niña conditions is estimated at approximately 64%, decreasing rapidly during the later northern spring. Probabilities for El Niño conditions are less than 10% through March-May 2011, exceeding 20% from the July-September season onward.

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