Nature Hits the 'Pause' Button On El Nino Development

The much-trumpeted development of an El Niño event in the tropical Pacific Ocean has become more muted in recent weeks, yet most signs still point to El Niño's eventual arrival, the National Oceanic and Atmospheric Administration (NOAA) reported on Thursday.

For several months now, climate forecasters have advertised a high likelihood of an El Niño event beginning in the fall or winter of 2014-2015. In the newest forecast, issued Thursday, NOAA experts and scientists at Columbia University's International Research Institute for Climate and Society said there is a 68% chance of an El Niño event starting in the northern hemisphere summer, with a higher chance, about 78%, that one will commence during the fall and early winter.

El Niño events are characterized by unusually warm ocean waters in the central and eastern tropical Pacific Ocean, and a range of related shifts in air circulation across the Pacific. These events have ripple effects around the world, from favoring flooding rains in parts of California to raising the odds of drought in Australia and Indonesia. They can also give an upward nudge to global average temperatures, combining with manmade global warming to lead to record warm years.

Computer model forecasts for El Nino during the next several months.

For these reasons and more, forecasters pay close attention to their development, sifting through climate clues from subsurface ocean temperatures in the tropical Pacific to trends in the trade winds that typically blow from east to west near the equator.

Right now, most of these clues suggest that El Niño is still on its way, but it is taking its sweet time, like a family on a summer roadtrip that keeps pulling off the highway at each rest stop.

Ocean temperature departures from average during June through July 2014. This shows the milder than average waters in the eastern tropical Pacific.

For example, subsurface temperature departures from average, which tend to be quite high when an El Niño event is developing, have dropped off in the past few weeks, and the atmosphere is not yet behaving like an El Niño is underway either.

With El Niño events, it takes two to tango â€" the air and the sea â€" and neither seems entirely sure that they want to dance quite yet.

Michelle L'Heureux, a scientist at NOAA's Climate Prediction Center in Maryland, says the development of El Niño has paused for a bit, which is not uncommon at this time of year. For example, she says a similar evolution happened in 2009, when a moderate El Niño developed after a summer in which the ocean and atmosphere couldn't quite get their act together.

Right now, some of the ingredients of El Niño are missing, such as weaker or even reversed trade winds (blowing from west to east instead of east to west) in the eastern and central tropical Pacific, and persistent thunderstorms in the central Pacific. However, there is an abundance of warmer-than-average water in the eastern tropical Pacific, which is a hallmark of El Niño, L'Heureux said.

Sea and air circulation during "neutral" conditions (top panel) and El Nino conditions (bottom panel.)

“El Niño is still likely here, yes we’re seeing a little bit of a structural slowdown but I also feel like this isn’t necessarily an unexpected thing,” she said. “For forecasters, these sort of peaks and valleys are sort of par for the course.”

El Niño is part of a larger cycle that involves the ocean and the atmosphere, and is known as the El Niño-Southern Oscillation, or ENSO. L'Heareaux told Mashable that the ocean part is halfway to El Niño, while the atmospheric part, the Southern Oscillation, isn't.

As NOAA explains in a post on its El Niño blog, the Southern Oscillation is "a seesaw in surface pressure between a large area surrounding Indonesia and another in the central-to-eastern tropical Pacific; it’s the atmospheric half of El Niño."

At this point, L'Heareaux says, “We’ve got the "EN," but we don’t have the "SO.""

While some El Nino researchers were speculating that a strong El Niño, comparable to a record event that occurred in 1997-98 and wreaked havoc on weather patterns worldwide, was on the way, NOAA and IRI said Thursday that this is most likely not the case. Instead, they are favoring a weak-to-moderate event.

L'Heareaux told Mashable that while the computer models that forecasters use to help predict El Niño events are "clustering" around a weak-to-moderate event, a strong event cannot be completely ruled out.

Subsurface water temperature anomalies in the Pacific Ocean, showing a big spike a few months ago, followed by more average temperatures in July 2014.

She says the models that suggested a strong event would occur are “Clearly backing off from that, although there’s still possible solutions here where you could get that.”

In addition to the uncertainty regarding El Niño's strength, forecasters have relatively low confidence in exactly when El Niño conditions will kick in.

L'Hearaux says the computer models are "awful" at pinpointing the moment of onset and the peak intensity of these events, but they show considerable skill at predicting events overall.

That, she says, is “So ironic, because those are the two pieces of info that people want to know.”