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Forecast Forum
MAY 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:
A
transition from La Niņa to ENSO-neutral conditions is expected
during June-
July 2008.
Discussion:
La
Niņa continued to weaken during May 2008, reflected mainly by changes in sea
surface temperatures (SSTs) across the equatorial
Pacific Ocean
.
Negative SST anomalies in the central and east-central equatorial Pacific
weakened, while the region of positive SST anomalies increased in the eastern
Pacific (Fig. T18).
The latest monthly SSTs in the westernmost Niņo-4 and Niņo-3.4 regions
are near 0.7°C below-average, and were near zero in the easternmost Niņo-3 and
Niņo 1+2 regions (Table T2).
Positive
oceanic heat content anomalies (average temperatures in the upper 300m of the
ocean) reflected the continuation of
above-average temperatures at thermocline depth in the west-central and eastern
equatorial Pacific (Fig. T17). However, a shallow layer of
negative anomalies (between the surface and 100m in the central Pacific)
continue to be sufficiently cool to maintain the below-average SSTs, which
support the atmospheric anomalies associated with La Niņa.
Enhanced low-level easterly winds and upper-level westerly winds
continued across the central equatorial Pacific (Figs. T20 and T21), while convection remained suppressed throughout the central equatorial
Pacific and enhanced over the far western Pacific (Fig. T25).
Collectively, these atmospheric and oceanic conditions continue to
indicate an ongoing, but gradually weakening, La Niņa.
A
majority of the recent dynamical and statistical SST forecasts for the Niņo
3.4 region indicate a transition to ENSO-neutral
conditions during June - August 2008 (Figs. F1- F13).
During the second half of the year, the majority of models reflect ENSO-neutral
conditions (−0.5 to 0.5 in the Niņo-3.4 region).
However, there is considerable uncertainty during this period as some
models suggest the possible development of El Niņo while others show a
re-development of La Niņa. Based on
current atmospheric and oceanic conditions and recent trends, a transition from
La Niņa to ENSO-neutral conditions is expected during June- July 2008.
Weekly
updates of oceanic and atmospheric conditions are available on the Climate
Prediction
Center
homepage (El
Niņo/La Niņa Current Conditions and Expert Discussions).
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www.nws.noaa.gov
