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ENSO Update

20 November 2008

Summary

The equatorial Pacific is presently ENSO-neutral. The equatorial Pacific region shows mainly below-average sea surface temperatures (SSTs) but the departure from normal is small. There is a 85 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 tropical Pacific are very weakly below-average. Above-average SSTs developed in the eastern equatorial Pacific in March, but they have weakened steadily over the last couple months and become very localized. On the other hand, the atmospheric anomalies would suggest that the tropical Pacific should be cool (or cooling), as the Southern Oscillation index has been persistently positive, and the low-level equatorial winds have been persistently easterly for more than a month. The oceanic response to these atmospheric changes has been extremely muted.

Out of a large set of dynamical and statistical forecast models, most models indicate ENSO-neutral SSTs during the coming Nov-Dec-Jan season. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of La Niña conditions is estimated at 13%, of El Niño conditions 2%, and the probability of maintaining ENSO-neutral conditions is 85% for the Nov-Dec-Jan season in progress.

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