ENSO Update

15 March 2006

Summary

General Discussion 

During February 2006, sea surface temperatures (SSTs) were approximately 0.5C below average in the central and eastern Pacific. The magnitude of the coldest SST anomalies declined slightly in February relative to January, but then slightly strengthened again in early March. The pattern of anomalies that had shifted westward into the central Pacific during January has moved back toward the eastern equatorial Pacific.

There appears to be sufficient changes in the upper ocean thermal structure, created by the low-level wind response to the SST anomalies over the last several months, to maintain the cool SST conditions at least through April 2006. Out of a large set of dynamical and statistical forecast models, most predict weak La Nina conditions continuing through March-April-May, and returning to ENSO-neutral conditions thereafter. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña event for March-April-May is approximately 53%, decreasing to 25% by mid-2006. The chances for developing El Niño conditions are estimated at approximately 2% through April 2006, increasing to 25% by mid-2006.

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