Current atmospheric and oceanic conditions in the tropical
Pacific are near average and do not support the development of either
La Niņa or El Niņo
in the next few months. Equatorial sea-surface temperature anomalies greater
than +0.5°C
persisted in the region west of the date line, while negative anomalies
remained in the eastern Pacific, near the South American coast (Fig.
1).
During July very little net change was observed in the SST anomalies in the
Niņo regions (Fig. 2).
Since late May positive equatorial upper-ocean temperature departures
have spread eastward into the central and eastern Pacific (see Fig. 3 for
evolution during July 2003). This evolving subsurface pattern is associated
with an eastward propagating oceanic Kelvin wave, resulting from a period of
weaker-than-average easterlies in the central equatorial Pacific that
occurred during late May and early June. SST anomalies in the Niņo
3.4 and Niņo
3 regions (Fig. 2) increased during early-June through early July, but then
decreased during the last half of July, as the equatorial easterlies
strengthened.
Some atmospheric indices, such as the Tahiti-Darwin SOI, and
central equatorial Pacific low-level (850-hPa) zonal wind and OLR, have
displayed considerable month-to-month variability since May 2003 and no
consistent trend towards either La Niņa
or El Niņo.
A majority of the statistical and coupled model forecasts indicate near
neutral conditions (Niņo 3.4 SST anomalies between -0.5°C and +0.5°C) for
the remainder of 2003 and early 2004. This is consistent with current
conditions and the lack of any consistent trends in the suite of oceanic and
atmospheric indices.
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