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ENSO Quick Look IRI ENSO Update / Prediction Technical ENSO Update IRI Probabilistic ENSO Prediction ENSO Prediction Plume Monthly archive ENSO Update21 April 2011SummaryThe moderate to strong La Niña conditions that were observed betweeen mid-August 2010 and early February 2011 have declined significantly to a weak level as of mid-April 2011, and neutral ENSO conditions are expected by mid-May. For the April-June season currently in progress, there is an approximately 48% probability for continuing La Niña conditions, and a 49% probability for returning to neutral ENSO conditions. Probabilities for La Niña conditions drop to just below 25% by the June-August season.General Discussion
In mid-April 2011, the NINO3.4 SST anomaly index has warmed to values
indicative of weak La Niña levels (0.6 degrees C below average),
while overall conditions below the ocean surface have warmed to become
slightly above average. However, zonal wind anomalies in the equatorial
Pacific continue to feature stronger than average easterlies, and
the Southern Oscillation Index continues to be well above average.
These observations indicate an uneven process of dissipation of the La
Niña, with oceanic aspects preceding the atmospheric aspects.
It is likely that the ENSO state, in terms of sea surface temperature
anomalies, will become neutral before mid-May. However, because of the
significant persistence of the atmospheric aspects during this episode's
dissipation, some of the climate conditions
associated with La Niña may continue through early June.
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