El Nino conditions are likely to
develop during September 2012
ENSO-neutral conditions continued during August 2012 despite
above-average sea surface temperatures (SST) across the eastern
Pacific Ocean (Fig.
1). Reflecting this warmth, most of the weekly Niņo index
values remained near +0.5°C (Fig.
2). The oceanic heat content (average temperature in the
upper 300m of the ocean) anomalies also remained elevated during
the month (Fig.
3), consistent with a large region of above-average
temperatures at depth across the equatorial Pacific (Fig.
4). Possible signs of El Niņo development in the atmosphere
included upper-level easterly wind anomalies and a slightly
negative Southern Oscillation Index. Despite these indicators,
key aspects of the tropical atmosphere did not support the
development of El Niņo conditions during the month. In
particular, low-level trade winds were near average along the
equator, and the pattern of tropical convection from Indonesia
to the central equatorial Pacific was inconsistent with El Niņo
with the typical regions of both enhanced and suppressed
convection shifted too far west (Fig.
5). Because of the lack of clear atmospheric anomaly
patterns, ENSO-neutral conditions persisted during August.
However, there are ongoing signs of a possibly imminent
transition towards El Niņo in the atmosphere as well as the
ocean.
Most of
the dynamical models, along with roughly one-half of the
statistical models, now predict the onset of El Niņo beginning
in August-October 2012, persisting through the remainder of the
year (Fig.
6). The consensus of dynamical models indicates a borderline
moderate strength event (Niņo 3.4 index near +1.0°C), while the
statistical model consensus indicates a borderline weak El Niņo
(+0.4° to +0.5°C). Supported by the model forecasts and the
continued warmth across the Pacific Ocean, the official forecast
calls for the development of most likely a weak El Niņo during
September 2012, persisting through December-February 2012-13
(see
CPC/IRI consensus forecast).
This
discussion is a consolidated effort of the National Oceanic and
Atmospheric Administration (NOAA), NOAA's National Weather
Service, and their funded institutions. Oceanic and atmospheric
conditions are updated weekly on the Climate Prediction Center
web site (El
Niņo/La Niņa Current Conditions and Expert Discussions).
Forecasts for the evolution of El Niņo/La Niņa are updated
monthly in the
Forecast Forum section of CPC's Climate Diagnostics
Bulletin. The next ENSO Diagnostics Discussion is scheduled for
4 October 2012. To receive an e-mail notification when the
monthly ENSO Diagnostic Discussions are released, please send an
e-mail message to:
ncep.list.enso-update@noaa.gov.
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