ENSO Update

18 April 2006

Summary

General Discussion 

During March 2006, sea surface temperatures (SSTs) were approximately 0.5C below average in the central and 1C below average in the eastern Pacific. The magnitude of the coldest SST anomalies increased slightly in March and shifted eastward relative to February, but then they had returned to near average by the end of March/early April. This return to neutral conditions occurred more rapidly than expected by any of the ENSO forecast models.
Currently, no substantial or structured SST anomalies exist in the tropical Pacific, with the exception of anomalies immediately off the coast of South America in excess of 3C below-average.

Previously existing large-scale perturbations to the upper ocean thermal structure have dissipated, strongly suggesting that neutral conditions will be in place at least through May 2006. Out of a large set of dynamical and statistical forecast models, most predict neutral conditions continuing throughout 2006. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña or El Nino event for April-May-June is much less than the climatologically expected odds of 25%. Neutral conditions are favored throughout 2006 starting with a 75% likelihood for Apr-May-Jun.

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