ENSO Quick Look
IRI ENSO Update / Forecast
Technical ENSO Update
IRI Probabilistic ENSO Forecast
ENSO Prediction Plume
Monthly archive

ENSO Update

18 December 2008

Summary

The equatorial Pacific is presently on the borderline of ENSO-neutral and weak La Niña conditions. The equatorial Pacific region shows mainly slightly below-average sea surface temperatures (SSTs). There is a 50 to 55 percent probability of ENSO-neutral conditions persisting over the coming season, and 45-50% for weak La Niña conditions.

General Discussion

Near average conditions have reigned in the tropical Pacific since early June, following the 2007/08 La Niña event, but during mid-December slightlyly below average SSTs re-emerged throughout the central tropical Pacific. A region of above-average SSTs that developed in the eastern equatorial Pacific in March have dissipated and become slightly below-average. Atmospheric anomalies have suggested 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 conditions has finally begun to appear.

Out of a large set of dynamical and statistical forecast models, more than half indicate ENSO-neutral SSTs during the coming Jan-Feb-Mar season, but a substantial minority indicate weak La Niña conditions. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of La Niña conditions is estimated at 48%, of El Niño conditions near 0%, and the probability of maintaining ENSO-neutral conditions is 52% for the Dec-Jan-Feb season in progress.

Top of Page