weekly report about El Nino and La Nina conditions (PDF, HTML),the sea surface temperature anomaly in the Nino 3.4 region reached minus 0.5 °C (see page 5 of 30) which is the threshold defining a La Nina.
However, similar or colder average temperatures have to exist in the equatorial Pacific for five consecutive overlapping three-month periods for the La Nina-like conditions to be declared a La Nina episode.
Although models are split, I think it is more likely than not that the conditions will actually become a La Nina episode. Note that the last complete 3-month period (MAM 2010) was still safely in the El Nino range, +0.8 °C!
The expected cooling may help to keep the average 2010 temperatures below those of 1998.
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