Cooling sea surface temperatures in the key Niño 3.4 region have touched the levels of early 2012.
Many have doubted forecasts calling for the onset of the first La Niña in almost five years, believing that its failure to materialize in convincing fashion last summer – as originally predicted – means that it may be off the table for 2016-17.
But in recent weeks, the oceans and atmosphere have been pulling everything into place to facilitate a potentially stronger La Niña than previously thought, so those who follow commodities markets may want to take a second look.
Last Thursday, the U.S. Climate Prediction Center reissued the La Niña watch that was removed in early September. The watch indicates that conditions are favourable for the phenomenon’s development within the next six months.
El Niño-Southern Oscillation, with its cool phase La Niña and warm phase El Niño, is one of the most reliable long-term indicators for global climate. The ENSO phases can have drastically different impacts on commodities worldwide – from energy use to grain yields.
La Niña, characterized by cooler-than-normal surface waters in the equatorial Pacific Ocean, has not officially been in place since the first quarter of 2012. But recently, cooling sea surface temperatures in the key Niño 3.4 region have touched the levels of early 2012 (reut.rs/2e2lI7y).
CPC now says there is a 70 percent chance that La Niña will develop during the Northern Hemisphere autumn 2016 and there is a 55 percent chance it will persist during winter 2016-17. This is up from last month’s forecast of a 40 to 45 percent chance of development.
The environment has not fully committed to the La Niña cycle for Northern Hemispheric winter as the sea surface temperature anomalies have at times hesitated to maintain the downward plunge.
But there are larger-scale features in the oceans and atmosphere that appear consistent with soon welcoming a full-on La Niña, rather than a borderline event or a neutral ENSO.
Over the past few months, there has been a considerable shift in the Pacific Decadal Oscillation or PDO, a large-scale, long-term climate variability in the North Pacific Ocean that is closely associated with ENSO cycles.
A positive PDO index is associated with anomalously cool waters and below-average sea level pressure in the interior North Pacific, while a negative PDO index is the inverse scenario. Positive PDO is often correlated with El Niño and negative PDO typically coincides with La Niña.
The PDO index has been unusually positive over the past two years, which is not surprising given the record-strong El Niño observed late last year. Since 1900, the first six months of 2016 and 2015 ranked third and fourth for highest average PDO index, behind 1941 and 1940 (reut.rs/2e2gB7l).
But the index has been on a steep decline over the past couple of months, and September’s reading of 0.45 was the lowest value since February 2014. PDO has not been negative since December 2013.
This substantial shift in overall oceanic-atmospheric conditions certainly makes a good case for La Niña, so a close watch on PDO trends over the next few months may hint at whether La Niña conditions could stick around, or whether neutral ENSO or a reversal back to El Niño is possible in 2017.