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Environment

Things Look El Niño-ish. But Things Could Change...

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In this animation of sea surface temperatures in the tropical Pacific Ocean between March and June, watch for a gradual warming in much of the region. (Source: NOAA Climate Prediction Center) In a previous post, I wrote that "El Niño's comin' (probably)." Now, it's probably not too much of a stretch to replace "probably" with "almost but not quite definitely." Some of the key aspects of an El Niño, which typically brings drought to some places, deluges to others, and a warmer globe overall, are now firmly in place. This prompted the U.S. Climate Prediction Center yesterday to up the odds of an El Niño occurring during summer in the Northern Hemisphere to 70 percent, and to 80 percent by fall and winter. Fixated as I was yesterday on convective mayhem in the Central U.S., I didn't have time to write about this right when the report came out. So you may have already heard the new El Niño news. But there's a bit of confusion out there about what's happening. So I thought I'd take a crack at explaining what's going on, with the help of some visuals.

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This animation shows how sea surface temperatures in the tropical Pacific between March and June varied from the long-term average. Watch for a band of anomalously warm water filling in most of the equatorial Pacific. (Source: NOAA Climate Prediction Center) For sure, many of the conditions are already in place. And as quoted by meteorologist Eric Holthaus yesterday in Slate, Kevin Trenberth of the National Center for Atmospheric Research is even saying, "Yes, we are into El Niño of sorts but it has not yet taken off in a major way that suggests strong coupling between the atmosphere and ocean has set in." My translation: The tropical Pacific Ocean looks El Niño-ish, but the atmosphere hasn't begun to fully respond accordingly.

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Source: NOAA What's up with the atmosphere? It turns out that the trade winds, which blow from east to west across the tropical Pacific, have not yet consistently weakened — as they typically do in the run-up to an El Niño. As Holthaus puts it:, "Once that happens, the upwelling of cold ocean water off the coast of South America is suppressed, and water temperatures at the surface will warm further, potentially unleashing a litany of effects across the globe." (Click on the thumbnail graphic for an illustration of the main ingredients of an El Niño, including the role of the trade winds.) So officially, El Niño is not here yet — and while the odds strongly favor its development, it may actually never get here. As Klaus Wolter of NOAA's Earth System Research Laboratory points out, on five occasions in the past when conditions in the tropical Pacific looked like they do now, four continued on as El Niño's. But on one of those occasions, in 1993, conditions dropped back down to "borderline neutral." The flip side of that coin is that on three of those occasions, the El Niño's that occurred were relatively strong, as assessed by a measure developed by Wolter called the Multivariate ENSO Index. Based on that measure, Wolter's independent assessment is that the odds of an El Niño occurring are at or above 80 percent through the rest of 2014. And with such high odds, he concludes that the "long anticipated breakthrough to El Niño conditions in 2014 is clearly under way, leading to the next question of how big it will get." His answer: The odds for a strong El Niño have increased now to "somewhere around 60 percent." Michelle L’Heureux, a climate scientist at NOAA’s Climate Prediction Center, expresses a bit more caution in a guest commentary for the Washington Post's Capital Weather Gang blog. She says that her CPC forecast team is confident that the chances are high for an El Niño. But computer modeling is equivocal about how strong it might be:

The ultimate strength of this El Niño – if one forms – is where the forecast team is the least confident. Looking purely at the model guidance, it appears that anything from a weak to a strong event is still in the cards . . . Yet, the forecast team tends to slightly favor a moderate-sized event (3-month average Niño-3.4 value, or ONI, between 1.0°-1.4°C) during the Northern Hemisphere fall and winter. However, the typical model errors for those longer forecast ranges imply a weaker (0.5°-0.9°C) or stronger event (1.5°C+) is still well within reach.

One thing is for sure: We'll be hearing a lot more about this in the coming weeks. Also, with El Niño-ish conditions already in place, Australia seems to be feeling some effects already.

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Maximum temperatures were warmer than the long-term average across much of Australia in May. (Source: Australia Bureau of Meteorology) As an update from the Australian Bureau of Meteorology put it earlier this week:

For Australia, El Niño is often associated with below-average rainfall over southern and eastern inland areas and above-normal daytime temperatures over southern parts of the continent. It is not uncommon to see some impacts prior to an event becoming fully established. May rainfall was below normal across parts of eastern Australia and maximum temperatures were above normal across much of the south and east.

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