CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
Alert System Status: La
expected to strengthen and last through the Northern Hemisphere winter 2010-11.
July 2010 La Niņa conditions developed, as negative sea surface temperature
(SST) anomalies strengthened across the central and eastern equatorial Pacific
Ocean (Fig. T18).
All of the Niņo indices decreased with values near -1.0°C in the Niņo
3 and 3.4 regions at the end of the month (Table T2).
The subsurface heat content (average temperatures in the upper 300m of
the ocean) continued to reflect a deep layer of below-average temperatures east
of the Date Line (Fig. T17).
Also convection was enhanced over Indonesia, while remaining suppressed
over the western and central tropical Pacific (Fig. T25). Enhanced low-level
easterly trade winds and anomalous upper-level westerly winds continued over the
western and central equatorial Pacific (Figs. T20,
T21). Collectively, these
oceanic and atmospheric anomalies reflect the development and strengthening of
La Niņa conditions.
Nearly all models predict La Niņa to continue through early 2011 (Figs.
However, there is disagreement among the models over the eventual
strength of La Niņa. Most dynamical models generally predict a
moderate-to-strong La Niņa, while the majority of the statistical model
forecasts indicate a weaker episode. Given the strong cooling observed over the
last several months and the apparent ocean-atmosphere coupling (positive
feedback), the dynamical model outcome of a moderate-to-strong episode is
favored at this time. Therefore, La
Niņa conditions are expected to strengthen and last through Northern Hemisphere
updates of oceanic and atmospheric conditions are available on the Climate
Niņo/La Niņa Current Conditions and Expert Discussions).