The short-lived La Niña

April 25, 2006

Today's Palm Beach Post has a front-page article on the La Niña that was declared in February and now appears to be near an end.  The article somewhat overates the importance of this.

Storm season may hing on Pacific's waters 

Ding-dong. La Niña's dead.

Or at least it's dying, which is a hint of good news for Floridians fretful about the coming hurricane season.

 La Niña is a pattern of cold water in the eastern Pacific that fosters hurricane-friendly winds in the Atlantic, often leading to seasons brimming with powerful storms. Federal meteorologists announced in February that La Niña had emerged for the first time since 2001, raising the prospect that this season could be even more hair-raising than the year of Katrina and Wilma.

Instead, they now say, La Niña appears to be vanishing after a brief, less-than-overpowering life.

"La Niña looks like it's at least flat-lining," said Klaus Wolter, a climatologist at the federal Earth System Research Laboratory in Boulder, Colo. Although that trend could reverse itself, "I'd say the stars are not quite aligned as badly for a big hurricane season as last year."…

One reason this isn't big news is that this was expected.  At the time La Niña conditions were declared, forecast models were already unaminous in predicting that it would end by hurricane season.  The hurricane season forecast issued by the Colorado State University team, which calls for another above-average season, followed that guidance.  

 The article goes on to hint one of the reasons why this isn't "Jump for joy, we're saved" sort of news: Last year's record breaking 2005 season featured "neutral" conditions, that is Sea Surface Temperatures in the area of interest were in between the extremes that define an El Niño or La Niña. The same was true for the busy 1995 season as well as the destructive 2004 season.

Put simply, there are other things going on that have an effect on tropical cyclone activity in the Atlantic.  Recent seasons have not hinged on the presence of a La Niña. 

It would be more notable if temperatures were to continue to rise sufficiently to trigger an El Niño.  Both below average seasons since 1995 (1997 and 2002) featured an El Niño in the Pacific.  There are a couple of models that suggest El Niño conditions towards the end of the season, but the majority are forecasting neutral conditions.


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