Sep 13, 2009

How Strong is This El Nino?

According to the Climate Prediction Center, El Nino is expected to strengthen and persist throughout the winter of 2009-2010. Recent sea surface temperature anomalies in the tropical Pacific would seem to support this:
As would the equatorial subsurface temperature anomalies:A broader look at subsurface temperatures (not just equatorial) however, shows a different story:This pattern is consistent with the cold phase of the Pacific Decadal Oscillation (PDO). When the PDO is cold, El Ninos tend to be weaker and shorter. The area of warm water at depth is seen to be only in a very narrow band right along the equator. This band becomes even narrower when looking at the anomalous depth of the 20C isotherm:It seems unlikely that this El Nino will strengthen especially given the near normal trade winds:
Because stronger than normal trade winds have generally prevailed since late 2006, warm water piled up in the western Pacific. The westerly equatorial counter current is what compensates for this effect. I suspect that much of the warm water in the eastern Pacific is due to an enhanced equatorial counter current:As Joe D'Aleo has pointed out, the warming of the Pacific is following a similar path to last year. La Nina returned and a cold and snowy winter for the Midwest and northeast followed. Even if this El Nino maintains itself through the winter, it is difficult too see how such a narrow band of deep warmth could have a strong impact. This along with a very quiet sun should give us another cold winter.

data from:

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