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Forecast Forum
SEPTEMBER 2010
Forecast Forum
The
CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
ENSO
Alert System Status: La
Niña Advisory
Outlook:
La Niña
is
expected to last at least into the Northern Hemisphere spring 2011.
Discussion:
La
Niña continued during September 2010 as reflected by the large expanse of
below-average sea surface temperatures (SSTs) across most of the equatorial
Pacific Ocean (Fig. T18).
All weekly Niño SST index values were between –1.3°C and –1.8°C at
the end of the month (Table T2).
In addition, the subsurface heat content (average temperatures in the
upper 300m of the ocean) remained below-average, reflecting a
shallower-than-average thermocline in the central and eastern Pacific (Fig.
T17). Convection remained
enhanced over Indonesia and suppressed over the western and central equatorial
Pacific (Fig. T25).
This pattern was linked to a continuation of enhanced low-level easterly
trade winds and anomalous upper-level westerly winds over the western and
central equatorial Pacific (Figs. T20,
T21).
Collectively, these oceanic and atmospheric anomalies reflect the ongoing
La Niña.
Consistent
with nearly all of the forecast models (Figs. F1-F13), La Niña is
expected to last at least into the Northern Hemisphere spring 2011.
Just over half of the models, as well as the dynamical and statistical
averages, predict La Niña to become a strong episode (defined by a 3-month
average Niño-3.4 index of –1.5°C or colder) by the November-January season
before beginning to weaken. Even
though the rate of anomalous cooling temporarily abated during September, this
model outcome is favored due to the historical tendency for La Niña to
strengthen as winter approaches.
Weekly
updates of oceanic and atmospheric conditions are available on the Climate
Prediction
Center
homepage (El
Niño/La Niña Current Conditions and Expert Discussions).
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www.nws.noaa.gov
