CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
ENSO-neutral conditions are
continue into Northern Hemisphere Fall 2008.
A transition from La Niņa to ENSO-neutral conditions
occurred during June 2008, as sea surface temperatures (SSTs) returned to
near-average across the central and east-central equatorial
(Fig. T18). Also, positive SST
anomalies continued in the eastern equatorial Pacific. Consistent with this pattern, the latest monthly SST index was -0.3°C in the Niņo-3.4 region, and +0.6°C in the Niņo 1+2 region (Table T2). The subsurface oceanic heat
content (average temperatures in the upper 300m of the ocean) and patterns of
subsurface temperature anomalies (Fig. T17) also reflected the transition to ENSO-neutral conditions. Positive heat
content anomalies were associated with above-average temperatures at thermocline
depth across the entire equatorial Pacific, while small negative subsurface
temperature anomalies persisted near the Date Line between the surface and 75m
Similar to past transitions, La Niņa continues to
linger in the atmospheric circulation, but with diminishing strength. Enhanced
low-level easterly winds and upper-level westerly winds remain across the
central equatorial Pacific (Figs. T20 and T21), while convection
continues to be suppressed in the central equatorial Pacific and slightly
enhanced over the far western Pacific (Fig. T25). Collectively, these atmospheric and oceanic anomalies are consistent
with a return from La Niņa to ENSO-neutral.
Most of the recent dynamical and statistical SST
forecasts for the Niņo 3.4 region indicate ENSO-neutral conditions
(−0.5 to 0.5 in the Niņo-3.4 region) will continue through Northern
Hemisphere Winter 2008-09 (Figs. F1- F13).
Despite this model consensus, the possible development of El Niņo or La
Niņa cannot be ruled out due to uncertainty in model forecasts and because ENSO
events often form during the second half of the year. Based on current
atmospheric and oceanic conditions, recent trends, and model forecasts, ENSO-neutral
conditions are expected to continue into Northern Hemisphere Fall 2008.
updates of oceanic and atmospheric conditions are available on the Climate
Niņo/La Niņa Current Conditions and Expert Discussions).