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ENSO Update

19 March 2008

Summary

La Niña conditions continue in the central and eastern equatorial Pacific. Below-average sea surface temperatures (SSTs) exist across nearly the entire equatorial Pacific, and fan out into the sub-tropical eastern Pacific. Based on the latest observations and forecasts, there is a 85% probability of maintaining La Niña conditions over the coming season.

General Discussion

The La Niña conditions that have been in place since August 2007, are indicated by substantially below-average sea surface temperatures in the central and eastern equatorial Pacific and reduced equatorial heat content. The oceanic manifestation of the current La Niña event has begun to show some signs of weakening over the last several weeks, suggested by a weakening of the cold anomalies, particularly those in the eastern equatorial Pacific. On the other hand, the Southern Oscillation Index used for monitoring the atmospheric manifestation of ENSO currently suggests strong La Niña conditions. Persistence of La Niña conditions is highly likely through at least the next couple months given the current magnitude and spatial extent of the anomalous atmospheric and oceanic conditions.

Out of a large set of dynamical and statistical forecast models, most models indicate continuation, but gradual weakening, of the strong La Niña conditions through 2008. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña is estimated at 85% for the Mar-Apr-May season in progress. The probability of returning to ENSO-neutral conditions increases to the climatological value of 50% toward the latter part of 2008.

Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.

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