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ENSO Update

18 September 2008

Summary

The equatorial Pacific is presently ENSO-neutral. Very weak below-average sea surface temperatures (SSTs) still exist near the dateline, and weak above-average SSTs are present in the eastern equatorial Pacific. There is a 90 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 developed in the eastern equatorial Pacific since March, but they have been weakening since mid-August. The low level zonal wind anomalies along the equatorial Pacific, and the Southern Oscillation index, and the thermocline depth anomalies all have been near average during the last couple months, albeit with some high frequency weather variability superimposed.

Out of a large set of dynamical and statistical forecast models, most models indicate ENSO-neutral SSTs during the coming Sep-Oct-Nov 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 5%, and the probability of maintaining ENSO-neutral conditions is 90% for the Sep-Oct-Nov season in progress.

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