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Forecast Forum
DECEMBER 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:
Developing
La Niña conditions are likely to continue into Northern Hemisphere Spring 2009.
Discussion:
During
December 2008, negative equatorial sea surface temperature (SST) anomalies
strengthened across the central and east-central
Pacific Ocean
(Fig. T18).
Correspondingly, the monthly SST index values were −0.4°C in Niño-1+2,
−0.5°C in Niño 3, −0.7°C in Niño 3.4, and −0.6°C in Niño
4 (Table T2). The
subsurface oceanic heat content anomalies (average temperatures in the upper
300m of the ocean) also became increasingly negative as below-average
temperatures at thermocline depth strengthened in the central and eastern
Pacific (Fig. T17).
Convection remained suppressed near the International Date Line, and
became more persistent near
Indonesia
during December (Fig.
T25).
Low-level easterly winds and upper-level westerly winds also strengthened
across the equatorial
Pacific Ocean
(Figs. T20
and T21)
. Collectively, these oceanic and
atmospheric anomalies reflect the development of La Niña.
Nearly
all of the recent forecasts for the Niño-3.4 region indicate a continuation of
below-average SSTs through the first half of 2009, with at least one-half
predicting La Niña conditions throughout the period (Figs. F1-F13).
While the magnitude of cooling remains uncertain, NOAA’s official La Niña
threshold (3-month average of the Niño-3.4 index less than or equal to
−0.5°C) is expected be met at least through January-March 2009.
Therefore, based on current observations, recent trends, and model
forecasts, La Niña conditions are likely to continue into the Northern
Hemisphere Spring 2009.
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
