Synopsis: ENSO-neutral
conditions are expected to continue during the next three months.
For the Pacific basin as a whole, oceanic and atmospheric conditions
continue to reflect the neutral phase of the ENSO cycle. However, sea
surface temperature (SST) anomalies in the equatorial Pacific increased
during April 2004 in the Ni�o
3.4 and 4 regions, and decreased in the eastern Pacific (Ni�o
3 and 1+2 regions, Fig. 1), as the equatorial cold tongue strengthened. By
the end of the month, positive SST anomalies greater than +0.5�C
(~1�F) were
observed in the region between
Indonesia and 180�W,
and negative anomalies (less than -2�C
in some places) were observed between 120�W
and the South American coast (Fig. 2). Since January 2004 equatorial Pacific
SST anomalies have been largest in the western portion of the basin. This
has resulted in an enhanced east-west gradient of SST, which has been
associated with stronger-than-average easterly winds over the central
equatorial Pacific (Fig. 3, top), enhanced precipitation over the western
equatorial Pacific (Fig. 3, bottom) and a steeper-than-average thermocline
slope in the central equatorial Pacific, as represented by positive
(negative) subsurface temperature departures in the western (eastern)
portion of the basin (Fig. 4).
Slightly more than half of the forecasts indicate near neutral conditions
in the tropical Pacific (Ni�o
3.4 SST anomalies between -0.5�C
and +0.5�C)
through the northern summer and early fall 2004. The remaining forecasts
indicate that El Ni�o
will develop within the next three-six months and intensify through the end
of the year. Many oceanic and atmospheric indices have displayed
considerable intraseasonal variability related to Madden-Julian Oscillation
(MJO) activity during the last several months, which together with the time
of year, may be contributing to the diversity of statistical and coupled
model forecasts for the tropical Pacific. Given the recent trends and
observed oceanic and atmospheric patterns discussed above, it is more likely
that ENSO-neutral conditions will continue for the next 3 months (through
July 2004). There is considerable uncertainty about what will happen after
July 2004.
This discussion is a consolidated effort of NOAA and its
funded institutions. Weekly updates for SST, 850-hPa wind, OLR and features of the equatorial subsurface
thermal 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 Ni�o/La Ni�a are updated monthly in the Forecast Forum
section of CPC's Climate Diagnostics Bulletin. To receive
an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send
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