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IRI ENSO Update / Prediction
Technical ENSO Update
IRI Probabilistic ENSO Prediction
ENSO Prediction Plume
19 May 2011
SummaryThe moderate to strong La Niña conditions that were observed betweeen mid-August 2010 and early February 2011 weakened during March and April, and dissipated to neutral conditions as of mid-May 2011. For the May-July season currently in progress, there is an approximately 24% probability for returning to La Niña conditions, a 63% probability for remaining in neutral conditions, and a 13% probability for the development of El Niño conditions. Neutral conditions are the most likely scenario throughout the remainder of 2011, although development of El Niño conditions or re-emergence of La Niña conditions cannot be ruled out.
In mid-May 2011, the NINO3.4 SST anomaly index warmed to values
indicative of ENSO-neutral levels (0.4 degrees C below average),
while overall conditions below the ocean surface have warmed to become
slightly above average. Zonal wind anomalies in the equatorial
Pacific no longer feature stronger than average easterlies, and
the Southern Oscillation Index has dropped to a neutral level.
These observations indicate that the major La Niña episode
of 2010/11 has ended, and cool ENSO-neutral conditions now prevail.
Because the atmospheric component of the episode was so strong
and long-lasting, however, some of the climate conditions associated
with La Niña may continue through early June.