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ENSO Update

19 August 2008

Summary

The equatorial Pacific is presently ENSO-neutral. Very weak below-average sea surface temperatures (SSTs) still exist near the dateline, and above-average SSTs are present in the eastern equatorial Pacific. There is a 80 percent probability of ENSO-neutral conditions persisting over the coming season.

General Discussion

Near average conditions have reigned in the tropical Pacific since early June, following the 2007/08 La Niña event. SSTs throughout the central equatorial Pacific are close to their long-term average values. Above-average SSTs have been seen in the eastern equatorial Pacific since March, but they been largely contained east of about 140W. The necessary growth in spatial extent or response of the atmosphere that could lead to El Niño conditions has not occured. The equatorial heat content is above average in the central and eastern equatorial Pacific, and this has helped maintain the above average SSTs in the eastern equatorial Pacific. However, the low level zonal wind anomalies along the equatorial Pacific, and the Southern Oscillation index, have been near average during the last couple months.

Out of a large set of dynamical and statistical forecast models, most models indicate ENSO-neutral SSTs during the coming Aug-Sep-Oct season. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of La Niña conditions is estimated at 5%, of El Niño conditions 15%, and the probability of maintaining ENSO-neutral conditions is 80% for the Aug-Sep-Oct season in progress.

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

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