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: La
conditions are expected by June 2011.
Niña continued to weaken during February 2011 as reflected by the reduced
strength of the negative surface and near-surface temperature anomalies across
much of the equatorial Pacific Ocean (Figs. T9
and T15). The Niño
indices were between 0.1°C and –1.3°C for the month of February (Table
Subsurface oceanic heat content anomalies (average temperatures in the
upper 300m of the ocean) returned to near zero in response to the eastward
progression of a strong oceanic Kelvin wave, which has weakened the negative
temperature anomalies at depth in the central and eastern equatorial Pacific (Fig.
T17). La Niña continued to be
most evident in the atmospheric circulation over the equatorial Pacific,
although at lesser intensity. Convection
remained enhanced over much of Indonesia and suppressed over the western and
central equatorial Pacific (Fig. T25). Also, anomalous low-level
easterly and upper-level westerly winds have persisted in this region (Figs.
However, a reduction in the strength of the anomalous low-level
cross-equatorial flow, and associated oceanic upwelling, over the eastern
Pacific contributed to anomalous SST warming in that region.
Collectively, these oceanic and atmospheric anomalies reflect a weakening
concurrence with the observed evolution, nearly all of the ENSO models predict
La Niña to weaken further in the coming months (Figs.
While the majority of models predict a return to ENSO-neutral by
May-June-July 2011 (three month average in the Nino-3.4 index between –0.5°C
and +0.5°C), there continues to be large uncertainty in the status of ENSO
through the Northern Hemisphere summer and fall.
Due to both model and observed trends, there is increasing confidence in
ENSO-neutral conditions by June 2011. However,
model forecasts issued in the spring typically have minimum skill (the “spring
barrier”), which results in low confidence forecasts for summer and beyond.
updates of oceanic and atmospheric conditions are available on the Climate
Niño/La Niña Current Conditions and Expert Discussions).