Current ENSO Information
ENSO Update
17 January 2003
Summary
The current El Ni�o 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 Ni�o 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 Ni�a 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 Ni�o, but could still be substantial
in some regions (as some already have been). Regions commonly affected by El Ni�o 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 Ni�o episode completes the mature stage. The
atmosphere continues to show many features indicative of El Ni�o, 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 Ni�o.
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 Ni�o.
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 Ni�o through March. By the June-July-August
period, the models diverge in opinion, with 29% calling for continuing weak El Ni�o conditions,
64% for neutral conditions and 7% for La Ni�a conditions.
(Note 1)
In summary, the models
suggest that this El Ni�o 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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