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El Niño / La Niña Current Conditions

The latest assessment of sea surface temperatures in the tropical Pacific by the Climate Prediction Center indicates that neutral ENSO conditions are occurring. As seen in the image below, the current anomalies do show indications of La Niña conditions with some cooler than normal sea surface temperatures developing from South America westward into the central Pacific Ocean.

A good way to monitor the El Niño/Southern Oscillation (ENSO) is through the use of the Multivariate ENSO Index (MEI). This index takes into account six variables including the sea-level pressure, zonal and meridional components of the surface wind, sea surface temperature, surface air temperature, and total fraction of the sky covered by clouds. Positive values of the MEI represent the warm ENSO phase (El Niño) while the negative MEI values represent the cold ENSO phase, (La Niña). As seen below the MEI is currently negative indicating La Niña conditions.

Comparing the current MEI to six other strong La Niña events since 1949, we see that as of early October 2007 the most recent MEI value has decreased to -1.11 into the moderate La Niña criteria. Compared to the six strong La Niña's, the current developing La Niña was a late starting event, but has quickly reached values last seen in late 1999 and early 1989. Despite the late onset, persistence will be very hard to beat for the next few months, therefore moderate La Niña conditions are expected to continue into the upcoming winter season.