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Notions of a Delayed La Nina Might Have Been Hasty


The decay of El Niño and the onset of La Niña, the cold phase of tropical Pacific Ocean surface temperatures, are occurring more rapidly than it would appear.

The timing of La Niña’s arrival is important to commodities markets as La Niña has vastly different effects on global climate than its warm counterpart, El Niño.

For example, in agriculture markets, if La Niña moves in on the early end of the range by June or July, U.S. summer crops could face complications with dry and hot weather. But dry regions of Australia, Southeast Asia, and Sub-Saharan Africa could receive ample rainfall prior to the peak of their next crop season.

The lingering of extremely warm waters in the equatorial Pacific Ocean has led to some flawed assumptions that El Niño is decaying at a slower pace than in previous years, and that the transition to La Niña will happen later than initially expected.

But the platform for La Niña’s entrance has been in the assembly phase since late last year, and new data suggests that construction is nearly complete.

There are a couple of key atmospheric and oceanic variables that we watch for to signal the switch from El Niño to La Niña, and now more than ever, these variables are pulling the final plugs on El Niño.

The cold pool just beneath the surface of the Pacific Ocean continues its rapid expansion, and it has nearly overcome the El Niño warmth on the surface, making remarkable strides in the final three weeks of March (http://tmsnrt.rs/1UDPlJr).

The anomaly lost heat during March at the same rate as in February, and decidedly cool waters now dominate the subsurface Pacific Ocean (http://tmsnrt.rs/1TwEjog).

A slowdown or reversal in this cooling trend does not seem likely as the atmosphere is becoming increasingly supportive of it. The Southern Oscillation Index, a measure of pressure tendencies over the Pacific Ocean, made a massive leap out of El Niño-favoring territory last month and is now ahead of the pace of similar years 1998 and 2010 (http://tmsnrt.rs/1TwETSN).

Another key supporting variable, trade winds in the western and central Pacific, no longer favor El Niño though they are not definitively in the La Niña camp, either. But if the SOI continues on its upward trend, the winds might be encouraged to strengthen, moving the Pacific Ocean closer to La Niña (http://tmsnrt.rs/1N5eMMe).

A graph of sea surface temperature anomalies in the defining Niño 3.4 region suggests that yes, 2016 is decaying at a slower rate than the other years.

But given both the record peak it is coming from and the recent changes in the ocean and atmosphere, it would actually not be surprising to see the transition happen just as quickly as in 1998, if we truly are to enter into a stronger La Niña (http://tmsnrt.rs/1N5ek0p).

Model glitch

Not only is the atmosphere supporting a faster switch to La Niña, but now so is a major climate model. It was announced last week that the Climate Forecast System Version 2 model, commonly known as CFSv2 and run by a division of the U.S. government, had accumulated an error that was massively skewing the results.

In a nutshell, the model built up an erroneous cold bias in the Atlantic Ocean which significantly altered global sea surface temperature forecasts. This bias has since been corrected, but before the correction, CFSv2 was one of the only models predicting a continuation of El Niño (http://tmsnrt.rs/1N5h4Lk).

Now the model predicts a healthy La Niña by July, further dismantling the delayed La Niña theory (http://tmsnrt.rs/1N5h1PA).

Source: AgWeek

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