Forecast Forum
AUGUST 2008
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.
Outlook:
ENSO-neutral conditions are
expected
to
continue
through
the
end
of
2008.
Discussion:
ENSO-neutral conditions continued during August 2008,
as recent increases in sea surface temperatures (SSTs) abated across the
equatorial
Pacific Ocean
. Above-average SSTs in the
east-central and eastern Pacific diminished, while below-average SSTs in the
central Pacific strengthened slightly (Fig. T18). From
west to east, the monthly SST index values range
from −0.3°C in the Niño-4
region to +1.1°C in the Niño 1+2 region (Table
T2). The
subsurface oceanic heat content (average temperatures in the upper 300m of the ocean) also decreased in response to the emergence
of negative temperature anomalies at thermocline depth in the east-central
Pacific (Fig. T17).
Although ENSO-neutral
conditions have been in place since June 2008, the atmospheric circulation over
the western and central tropical Pacific continues to reflect lingering aspects
of La Niña. Enhanced low-level
easterly winds and upper-level westerly winds persist in this region (Figs. T20 and T21), while convection remains
generally suppressed over the central Pacific (Fig. T25). Despite
this lingering La Niña signal in the atmosphere, the overall atmospheric and
oceanic system is consistent with ENSO-neutral conditions.
Most of the dynamical and statistical SST forecasts
for the Niño
3.4 region indicate a continuation of ENSO-neutral conditions
(−0.5°C to 0.5°C in the Niño-3.4 region) through the Northern Hemisphere Spring 2009 (Figs.
F1- F13). While the model spread
continues to include the possibility of an El Niño, the decrease in subsurface
and surface temperatures makes this outcome unlikely during the next several
months. In addition, the
redevelopment of negative temperature anomalies at thermocline depth and the
historical tendency for multi-year La Niña episodes means that even a return to
weak La Niña conditions is possible. However,
based on current atmospheric and oceanic conditions, recent trends, and model
forecasts, ENSO-neutral conditions are expected to continue through the end of
2008.
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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