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 Niña Watch
is expected to continue into the Northern Hemisphere fall 2011, with ENSO-neutral
or La Niña equally likely thereafter.
July 2011, ENSO-neutral was reflected in the overall pattern of small sea
surface temperature (SST) anomalies across the equatorial Pacific Ocean (Fig.
All of the monthly weekly Niño index values were generally near average
(Table T2), ranging from –0.3°C (Niño-4) to 0.5°C (Niño-1+2).
However, the subsurface oceanic heat content anomaly (average temperature
anomalies in the upper 300m of the ocean) continued to weaken and is currently
near zero, which reflects the strengthening of the below-average temperatures at
depth in the east-central Pacific Ocean (Fig. T17). The
atmospheric circulation anomalies were more variable during the past month, but
the monthly means still reflect aspects of La Niña.
For example, convection continued to be enhanced over eastern Indonesia
and Papua New Guinea, and generally suppressed over the central equatorial
Pacific, mainly south of the equator (Fig. T25).
Also, anomalous low-level easterly and upper-level westerly winds
persisted over the central tropical Pacific (Figs. T20,
Thus, while tropical Pacific oceanic anomalies indicate ENSO-neutral, the
atmospheric patterns continue to reflect La Niña-like conditions.
majority of ENSO models, and all multi-model average forecasts (indicated by
thicker lines, Figs. F1-F13),
indicate ENSO-neutral will continue into the Northern Hemisphere fall 2011
(three-month average in the Nino-3.4 index between –0.5°C and +0.5°C).
Beyond the early fall, the forecasts are less certain with half of the
models persisting ENSO-neutral conditions continuously through early 2012.
Along with a few other models, the latest runs from the NCEP Climate
Forecast System (CFS) models predict La Niña to re-develop during the fall.
This forecast is also supported by the ongoing La Niña-like tropical
atmosphere, subsurface temperature trends, and the historical tendency for
significant wintertime La Niña episodes to be followed by relatively weaker La
Niña episodes the following winter. Therefore,
ENSO-neutral is expected to continue into the Northern Hemisphere fall 2011,
with ENSO-neutral or La Niña equally likely thereafter.
updates of oceanic and atmospheric conditions are available on the Climate
Niño/La Niña Current Conditions and Expert Discussions).