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ENSO Update

17 January 2003

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> General Discussion
 

Summary

The current El Niņo will very likely continue at least through February 2003, followed by 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 than those experienced during the strong 1997-98 El Niņo, but could still be substantial in some regions (as some already have been). Regions commonly affected by El Niņo at this time of year should remain alert to the possibility of such climate effects.

 

General Discussion

Between mid-December and mid-January, sea surface temperatures (SSTs) in most of the east-central equatorial Pacific remained more than 1 degree C above normal. In the central/eastern basin (east of the dateline), SSTs have exceeded 2 degrees C above normal. During this period, most SSTs became slightly less warm than they were during the mid-November to mid-December period. In particular, in the last half of December warmer than normal SSTs in the central Pacific weakened, and in the first half of January those in the eastern part of the basin weakened. SSTs off the west coast of South America weakened to less than one-half degree above normal during early January. These far eastern SSTs could, however, warm to farther above normal again over the coming two months as the El Niņo episode completes the mature stage. The atmosphere continues to show many features indicative of El Niņo, including reduced easterly trade winds in the western and central tropical Pacific, a lower than average Southern Oscillation Index, and above average tropical rainfall from 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 29% calling for continuing weak El Niņo conditions, 64% for neutral conditions and 7% 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.

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