Warmer-than-normal sea surface and subsurface
temperatures were observed throughout most of the equatorial Pacific during April 2002.
Sea surface temperature anomalies were up to 2°C warmer than average in the region
between the Galapagos Islands and the South American coast, and greater than 1°C warmer
than average immediately to the west of 180°W (Fig. 1).
Although there was considerable warming in the eastern equatorial Pacific during
February-April, which resulted in locally heavy rainfall along the coasts of Ecuador and
northern Peru, there was little change in SSTs or subsurface temperature anomalies in
regions father west during this period. Consistent with this lack of evolution in the
central equatorial Pacific, atmospheric indices for low-level winds, sea level pressure
(SOI) and precipitation (OLR) continue to indicate near-normal conditions.
The Madden-Julian Oscillation (MJO) is an important source of variability that can
contribute to a more rapid evolution toward El Niņo through related fluctuations in
low-level winds and precipitation over the western and central equatorial Pacific. An
eastward-propagating oceanic Kelvin wave, initiated by strong MJO activity in late 2001,
resulted in the rapid warming that was observed along the coasts of Ecuador and northern
Peru in early February. Since that time MJO activity has weakened and there has been no
additional significant Kelvin wave activity. Without such activity a slow evolution
towards El Niņo conditions is possible through the remainder of 2002.
This assessment agrees well with several coupled model and statistical forecasts, which
indicate a gradual warming over the next several months with weak-to-moderate El Niņo
conditions by the end of 2002. It is important to add that a weak or moderate El Niņo
would feature considerably weaker global impacts than were experienced during the very
strong 1997-98 El Niņo.
This discussion is a team effort of NOAA and its
funded institutions. Updates of SST, 850-hPa wind, OLR and the equatorial subsurface
temperature structure are available on the Climate Prediction Center web page 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. To receive
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