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La Nina Part II

By Joe D'Aleo
Monday, December 29, 2008

Last winter, we experienced a La Nina, strongest since 1988.

Most strong La Ninas are multi-year events especially during the cold Pacific Decadal Oscillation stages as we had from 1947-1977 (and again after 1998)

This can also be seen in the plot of Wolter’s Multivariate ENSO Index (MEI).

Usually the second year is weaker.

We see the eastern Pacific warmth in late June.

See animated tropical temperatures over the last year here. It shows the strong La Nina weaken and warming take place in the eastern Tropical Pacific before cooling resumed.

The water beneath has cooled dramatically on recent months with readings as much as 5C below normal. Easterly winds will cause upwelling of this cold water and increased strength of La Nina in the next few months into the boreal spring.

The cooling is reflected in the heat content near the equator from the dateline to 100W longitude with levels comparable to last December.

Most ENSO models suggest at least a weak La Nina returns for winter and early spring.



December so far has had cold weather central.



Similar years with a cold Pacific, warm Atlantic, westerly QBO and lower solar activity had January’s like the following with more cold central.



Should La Nina come on stronger than the models (except for the CFS) suggest, more southeast warming would be likely in the extreme like 1974 and 1976.