Since August 2000, sea surface
temperature (SST) anomalies have gradually decreased throughout the equatorial Pacific (Fig. 1). Consistent with this anomalous cooling, the low-level
easterly winds have increased in strength over the central and western equatorial Pacific
and the Southern Oscillation Index (SOI) has significantly increased. The accompanying
pattern of tropical rainfall anomalies, which is drier-than-normal conditions over the
equatorial central Pacific, has also strengthened during this period (Fig.
2). This strengthening of the cold episode conditions is also evident in the
subsurface ocean temperature anomalies, with negative anomalies of at least -3C now
evident in the eastern equatorial Pacific (Fig. 3).
Since 1997, the evolution of many atmospheric and
oceanic indices is remarkably similar to that observed during the 1982-1986 period, when a
strong El Niņo was followed by three years of cooler-than-average- conditions in the
tropical Pacific. Many indices show distinct annual cycles during these cold episode
periods, with the northern winter seasons featuring 1) minima in the SST indices, 2)
maxima in the SOI, and 3) maxima in the low-level easterly and upper-tropospheric westerly
wind anomalies over the central equatorial Pacific (Fig. 4).
The most recent NCEP coupled model and statistical model forecasts, as well as other
available forecasts, indicate that cold episode conditions will weaken during the next 3
months, followed by near-normal conditions during March-May 2001. However, during recent
months each successive forecast has tended to persist the cold episode conditions longer
that previous forecasts, thereby delaying the transition from cold episode to
near-neutral. The lack of any significant eastward shift of the subsurface warm pool in
the western equatorial Pacific during recent months suggests that the cold episode will
linger into the northern spring. Average La Niņa impacts can be expected over Indonesia/
northern Australia, Northeast Brazil and southern Africa (all wetter than normal) during
the next three months. However, due to ongoing Madden-Julian Oscillation (MJO) activity,
there is likely to be considerable temporal rainfall variability in these regions, and
many other tropical and subtropical regions through March 2001.
Weekly updates for SST, 850-hPa wind, and OLR are
available on the Climate Prediction Center homepage
at: http://www.cpc.ncep.noaa.gov (Weekly Update).
Forecasts for the evolution of El Niņo/La Niņa are updated monthly in CPC's
Climate Diagnostics Bulletin Forecast Forum.
This ENSO Diagnostic Discussion, which replaces the ENSO Advisories, will appear
regularly around the 10th of each month on the CPC web site.