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ENSO Update

17 May 2006

Summary

Neutral conditions exist in the tropical Pacific. As of mid-May sea surface temperatures are within 0.5C of average across the equatorial Pacific. Based on the latest observations and forecasts, the probability of neutral conditions continuing through the May-June-July 2006 season is approximately 90%.

General Discussion

In early April 2006, sea surface temperatures (SSTs) returned rapidly from about 0.5 C below average to very near-average temperatures in the central-eastern Pacific. Temperatures have remained very close to their long-term average over the last month. The return to neutral conditions in April occurred more rapidly than expected by any of the ENSO forecast models, and some of the forecast models still do not represent the current neutral state in their initial conditions. Currently, no substantial or structured SST anomalies exist in the tropical Pacific.

Large-scale perturbations to the upper ocean thermal structure observed in early 2006 have completely dissipated, suggesting that neutral conditions will be in place at least through mid-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 conditions for May-June-July is much less than the climatologically expected odds of 25%. Neutral conditions are favored throughout 2006 starting with a 90% likelihood for May-Jun-Jul.

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

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