La Niña Clearly In Command

It took nearly forever to arrive, but with the Southern Oscillation Index (SOI) at a hefty value of +14.9, La Niña now seems solidly in charge:

A La Niña event is firmly established in the Pacific, strengthening over the past month and contributing to the enhanced eastern Australian rainfall since November.

Cooler than average sea surface temperatures (SSTs) now extend further west along the equator than at any time since 2000, while warmer than average SSTs surround northern Australia. The December 2007 Southern Oscillation Index (SOI) of 14.4 is the highest monthly SOI value since April 2006. Trade Winds remain enhanced and cloudiness continues to be suppressed along much of the central equatorial Pacific; both indicators of the now mature event. While sub-surface temperatures remain cooler than normal in the east, some warming has occurred in the western regions.

Although some computer models suggest that the event is nearing its peak, most continue to indicate the persistence of cool Pacific Ocean temperatures, consistent with a La Niña, until at least autumn 2008.