CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
Alert System Status: Final
conditions have developed and are expected to continue at least through the
Northern Hemisphere summer 2011.
transition from La Niña to ENSO-neutral conditions occurred during May 2011 as
indicated by generally small sea surface temperature (SST) anomalies across the
equatorial Pacific Ocean east of the Date Line (Fig. T18). The May Niño index values (Table T2)
were slightly below-average in the central and east-central equatorial Pacific
(Niño-4 index of –0.5°C and Niño 3.4 index of –0.5°C), and above-average
SSTs in the eastern equatorial Pacific (Niño-1+2 index of +0.8°C).
The subsurface oceanic heat content anomalies (average temperatures in
the upper 300m of the ocean) remained elevated, but relatively constant during
the month, reflecting a large area of above-average temperatures at depth (Fig.
Consistent with other transitions to ENSO-neutral conditions, the
atmospheric circulation anomalies continued to show some features consistent
with La Niña, albeit at weaker strength. Convection
was enhanced over eastern Indonesia and suppressed over the central equatorial
Pacific (Fig. T25).
Also, anomalous low-level easterly and upper-level westerly winds
weakened but persisted over the central Pacific (Figs. T20,
Collectively, these oceanic and atmospheric anomalies reflect a
transition to ENSO-neutral conditions, but with lingering La Niña-like
atmospheric impacts, particularly in the global Tropics.
observed trends, along with forecasts from a majority of the ENSO models,
indicate ENSO-neutral will continue through the Northern Hemisphere summer 2011
(three-month average in the Nino-3.4 index between –0.5°C and +0.5°C; Figs.
Thereafter, most models and all multi-model forecasts predict ENSO-neutral
to continue through the remainder of 2011. However,
the status of ENSO beyond the Northern Hemisphere summer remains more uncertain
due to lower model forecast skill at longer lead times, particularly during this
time of year.
updates of oceanic and atmospheric conditions are available on the Climate
Niño/La Niña Current Conditions and Expert Discussions).