Current ENSO Information

ENSO Update

21 February 2003

Summary

The current El Niņo will very likely show significant weakening or dissipation during the March to June period. The outlook beyond June 2003 is more uncertain. Based on the behavior of past El Niņo events and current model forecasts, it is most likely that conditions will be near-neutral during the second half of 2003, although the development of La Niņa conditions is slightly greater than in an average year. During the coming 1 to 3 months, climate effects in most regions are most likely to be weaker for the current El Niņo than those experienced during the same season in 1998 when the strong 1998 El Niņo was reaching its end, but they could still be substantial in some regions.

General Discussion

Between mid-December and mid-February, sea surface temperatures (SSTs) in much of the east-central equatorial Pacific remained more than 1 degree C above normal. During the last few weeks, SSTs in the eastern equatorial Pacific have been decreasing. SSTs off the west coast of South America weakened are now beginning to show signs of being lower than normal. Despite this cooling trend, the atmosphere continues to show features indicative of El Niņo, such as a slightly lower than average Southern Oscillation Index and above average tropical rainfall from about 170E to 155W longitude. The above features are consistent with the mature stage of El Niņo.

SST forecasts from a large set of dynamical and statistical models indicate that we are near the end of the mature stage and beginning the declining phase of this moderate El Niņo. Relatively high skill is expected for the first two to three months of the model forecasts at this time of the year, followed by lower skill from May onward. Nearly all of the models indicate a continuation (but weakening) of the El Niņo through March. By the June-July-August period, the models diverge in opinion, with 20% calling for continuing weak El Niņo conditions, 67% for neutral conditions and 13% for La Niņa conditions. (Note 1) In summary, the models suggest that this El Niņo episode will likely continue through March, and possibly into April or May before likely weakening to neutral levels. The outlook for middle and later 2003 currently has high uncertainty.

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