El Nino starts to stir

The Southern Oscillation Index has been hanging in El Nino territory for the past month, but scientists will need a little longer before they're able to announce the weather phenomenon's return.

Climate Central

El Nino watchers, rejoice (maybe). A weak El Nino has formed (sorta).

On Tuesday, researchers at the International Research Institute for Climate and Society said a borderline El Nino is upon us, with the odds for further development increasing throughout the fall and winter. 

Figure 1: Chart showing ocean temperatures in different regions of the Pacific used to gauge El Nino, including the recent rise in temperatures.

Credit: IRI

This El Nino has played a game of hide and seek since an El Nino Watch was declared way back in March. After picking up steam in the spring and early summer, El Nino conditions essentially disappeared in July and much of August.

But the telltale signs of El Nino are starting to re-emerge. Ocean temperatures in the tropical Pacific, which tend to warm during an El Nino, have reached the threshold last week typically used to declare El Nino has arrived.

“Borderline El Nino conditions have now returned in both ocean and atmosphere, after a 2-month hiatus,” said Tony Barnston, IRI’s chief forecaster.

And the running average of the Southern Oscillation Index, an atmospheric measure of El Nino, has also been hanging in El Nino territory for the past month according to Australia’s Bureau of Meteorology.

So why aren’t scientists shouting from the roofs that El Nino is here and ready to shift weather patterns around the globe?

“We would have to see temperatures at this level for about a month before we declare we have El Nino conditions,” said Dan Collins, a scientist with the Climate Prediction Center, in a separate call with reporters.

Precipitation patterns over the tropical Pacific also haven’t quite lined up yet.

But El Nino-like impacts aren’t necessarily waiting for scientists to officially declare the climate phenomenon here. In fact, Collins said some impacts are already being seen in the US. Those include a decrease in hurricane activity in the Atlantic basin and an uptick in activity in the eastern Pacific, including tropical storms that have brought heavy rain to the Southwest recently. El Nino also tends to ramp up global temperatures, and according to numbers also released on Tuesday, this was the hottest summer ever recorded for the planet.

IRI’s forecast, which is issued in conjunction with CPC, shows the odds of El Nino fully developing and persisting from November-March are between 70-75 per cent, up a few notches from their forecast issued earlier this month. Most models are still showing a weak-to-moderate event is likely. The main wrinkle that could put the kibosh on an El Nino is a shift in low level winds that could dissipate the warm surface waters. Barnston said that forecasters aren’t expecting that to happen, though.

Figure 2: A graph showing the likelihood of El Nino conditions over consecutive 3-month periods.

Source: IRI

Asked for a corollary for such a late-blooming El Nino, Barnston said it resembled 1986.

“We had a late-developing El Nino in 1986, and that ended up becoming a moderate El Nino and lasted a second year because it couldn’t run its course in a seasonal time window like they usually do,” he said.

However, Barnston was quick to point out that if this El Nino forms, there’s no guarantee it would also be a multi-year event.

The other quirk to this year’s burgeoning El Nino is where the warmest waters are located. They currently sit in the central Pacific, a little west of where El Nino typical forms. If El Nino does form there, it would be a different flavor, known as El Nino Modoki. Some research has indicated that climate change could be upping the odds of Modoki – Japanese for similar but different – events.

But for now, researchers are focused on seeing if this El Nino finally comes out to play. And they'll have a better sense of that in two weeks when CPC and IRI release their official update.

Originally published by Climate Central. Reproduced with permission.