Current Information
ENSO Update
16 October 2002
Summary
The IRI's assessment is that there is a nearly 100% probability that
El Niño conditions will continue for the remainder of 2002 and into
early 2003. This assessment is based on the collective forecasts of various
ENSO prediction models, as well as on the experience of the several oceanographers
and atmospheric scientists familiar with the El Niño phenomenon.
This probability is the same as that given one month ago. Substantially
warmer than average sea surface temperatures that first emerged in late
May are nearly certain to continue for the next 4 to 8 months. It is most
likely that this will be a moderate El Niño, which is significantly
less strong than the 1997-98 event. The associated climate effects in most
regions are expected to be weaker than those associated with the 1997-98
El Niño, but may nonetheless be substantial in some regions.
General Discussion
Between mid-September and mid-October, sea surface temperatures (SSTs)
in most of the east-central equatorial Pacific remained above 1 degree
C above normal, with strongest positive anomalies between 1.5 and 2.5 degrees
C over the central basin just east of the dateline. Slightly below normal
SST continues in the far eastern Pacific, but has warmed somewhat over
recent weeks. The warm anomalies in the NINO4 and NINO3.4 regions for September
averaged near or just above 1 degree, while in the NINO3 region SST averaged
about 0.7 degrees above normal. The relatively cooler eastern SST is expected
to warm further over the coming several months as the El Nino episode matures.
The atmosphere continues to show all features indicative of El Niño,
including persistent westerly wind anomalies in the western and central
tropical Pacific, a lower than average Southern Oscillation Index, and
anomalous equatorial convection stretching from 150E to 160W longitude.
Negative SST anomalies and precipitation anomalies continue in parts of
the far western Pacific and Indonesia. All of the above features indicate
that the El Niño is progressing toward maturity.
SST forecasts from a large set of dynamical and statistical forecast
models support the interpretation that we are witnessing the evolution
of El Niño into the mature phase of a moderate episode. Relatively
high skill is expected for the model forecasts at this time of the year.
Depending on the type of forecast model, between 93 and 100% of the models
predict El Niño conditions persisting into the December-January-February
period and continuing into early Northern Hemisphere spring of 2003. The
remaining models call for near-neutral SST throughout 2002. (Note
1) Thus, overall, the models suggest that we are in a maturing El Niño
episode that will continue into at least early 2003.
Note 1 - Only models that produce
a new ENSO forecast every month are included in the above statement.
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