El Nino

3 MARCH 2006



World Meteorological Organization

EL NIÑO/LA NIÑA
UPDATE

Current Situation and Outlook

Since around the turn of the year, sea-surface temperatures (SSTs) in the central and eastern equatorial Pacific have ranged between half and one degree Celsius below normal. Combined with broader tropical Pacific ocean and atmosphere conditions, this is consistent with the early stages of a basin-wide La Niña event. However, the development of basin-wide La Niña conditions at this time of the year is highly unusual, hence there is some additional uncertainty over the extent to which typical La Niña rainfall and temperature patterns will occur for this event. Furthermore, the La Niña conditions are expected to be relatively short-lived, with a return to neutral conditions across the equatorial Pacific likely by mid-year or shortly thereafter.

At this time of the year, a continuation, or persistence, of prevailing conditions in the tropical Pacific is least likely, with the March to May period often witnessing marked transitions between phases of El Niño/La Niña. Although most computer models and expert interpretation project La Niña conditions to continue, at least through the next couple of months, a return to neutral conditions is considered most likely by mid-year. As predictions are least reliable at this time of year, careful monitoring will be needed over the next several months for indications of La Niña conditions persisting further into the year, or of the onset of a rapid evolution toward El Niño conditions. Neither of these two scenarios is considered likely, but cannot be ruled out at the current time.

SSTs first became colder than normal close to the South American coast in September 2005.   This likely influenced local climate patterns through the latter months of 2005, but did not at that time constitute a basin-wide La Niña event. While conditions remained mostly neutral in the central equatorial Pacific, SSTs in the western... [continues]

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