The current La Niña event was successfully predicted starting with our first ENSO forecast issued in February 2007. Note that the forecast was made before the so-called “spring barrier,” when predicting the evolution of ENSO was most difficult. At that time, the overwhelming majority of the models employed by IRI and CPC were predicting ENSO-neutral conditions. 

The CPC was quite slow in recognizing the developing La Niña conditions in 2007. Even in their July 2007 diagnostic discussion they called for "ENSO-neutral conditions to continue during the next 2 months, with ENSO-neutral or La Niña conditions equally likely thereafter." That outlook, as well as a weakening of the easterly winds in the western equatorial Pacific in July and August (see our review), somewhat affected our judgment on the magnitude of the event.

A sharp acceleration of La Niña development since August 2007 caught many by surprise. For example, Klaus Wolter (NOAA) wrote on his ENSO monitoring website: “I have to admit that the drastic drop in the MEI [Multivariate ENSO Index] since August was quite unexpected.”  In February 2007, the standardized Southern Oscillation Index (SOI) reached 2.7, the highest value since November 1973, and the SST anomaly in the Niño 3.4 region was -1.89°C, the lowest value since January 1989. 

There is no single classification of ENSO events in terms of their intensity. In the latest diagnostic discussions, the CPC refers to the current La Niña event as “moderate-to-strong.” As for the MEI, it is right at the moderate La Niña threshold. Its current values are similar to those during the prolonged La Niña episode of 1998-2001. Substantial cooling in the equatorial Pacific contributed to the decline in global temperature (see our post-mortem analysis for the Northern Hemisphere).