An illustrated guide to 100 percent chance of El Niño
NOAA’s El Niño forecast is out today, and it will be no surprise to anyone paying even the slightest bit of attention that…
- El Niño is getting stronger,
- there’s a 100 percent chance that it will continue through at least the December–February season, and
- the odds of it becoming the strongest event on record by the October-December season (as ranked by the 3-month average Relative Oceanic Niño Index) are now 75 percent.
In a minute, I’ll walk you through a photo dump of key El Niño graphics that explain what’s going on in the tropical Pacific Ocean and why forecasters are so confident in their outlook. But in case you’re new here, and what you’re really wondering is why everyone from your TV weathercaster to your Uncle Bob will.not.shut.up about El Niño, it’s because El Niño affects seasonal hurricane activity. And tornadoes (part 1 and part 2). And high-tide flooding. And atmospheric rivers, which can be drought-busters (yay!) or dam-busters (boo!). And salmon populations. And surfing in Hawaii. And coral bleaching. And snowfall in North America. And fires in California. And that’s just a partial list!
So…you’re saying there’s no chance?
It’s not unprecedented, but it is uncommon to catch an ENSO forecaster telling you the odds of a particular climate outcome are literally, flat out, not hedging a single bet, 100 percent. But that’s where we are with the El Niño forecast for the next ~6 months: 100 percent chance of El Niño through the January-March season. Just look at all these red bars. It’s like somebody just learned how copy and paste shortcuts work and got carried away.
Now, the ENSO Blog has spent a fair amount of time over the years explaining why climate scientists can rarely say with 100 percent certainty what the climate system is going to do. We’ve hammered that “uncertainty is the norm” point home so hard over the years that we surely need to explain why forecasters have thrown their normal caution to the wind.
I posed that question to Emily Becker, our ENSO blog lead, in our biweekly check in meeting. Here’s how it went.
Rebecca: Explain yourself! I’ve spent all these years as your editor trying to help you explain to people that we can’t predict the climate with 100 percent certainty, but that forecasts don’t have to be perfect to be useful, and blah, blah, blah, and now NOAA’s ENSO forecasters give us this: 100 percent chance. It’s sus. Clearly, you’ve been holding out on us. Why now?
Emily: Srsly? You amateurs are never satisfied. We give you what you said you want—100 percent certainty—and you grouse about it. I can’t even with you people.
[Editor’s note: Emily says my recollection of that part of our conversation is maybe not 100 percent accurate. I refuse to let AI notetakers snoop on our meetings, however, so we can never be 100 percent certain. We agreed to disagree.]
After she gave me sass, Emily did explain that the high level of certainty comes from the well-established coupling between the ocean and the atmosphere in August. This coupling, in which the atmosphere and the ocean are both doing things that push the system in the same direction—a feedback loop—is the heart of ENSO and what makes it predictable months in advance. Once the two are strongly in sync, their joint momentum is virtually impossible to disrupt on the seasonal time scales. Between July and August, evidence of that momentum was everywhere you looked. So let's look.
Surface waters in the tropical Pacific got hotter
No matter which way we look at it, the tropical Pacific Ocean is hot. Here’s the glamour shot, showing how much the ocean has warmed up in the past month. This is regular sea surface temperature anomaly, the difference from the long-term average (1991-2020). Grab the slider and drag to compare August to July.
Grab and drag the slider to see how sea surface temperatures climbed even farther above average (1991-2020) in the tropical Pacific Ocean between July (left map) and August (right map). Climate.us maps, based on OISST data from NOAA.
As Emily explained last month, we can no longer use only the plain anomaly to understand the true strength of El Niño in a warming world, so we also have to consider the anomaly relative to the whole tropics. When we subtract the tropics-wide average anomaly from the anomalies in the Pacific, it’s clear that the El Niño sweet spot (black outline) is not just warmer than average, it’s also much warmer than the western Pacific.
7-day average temperatures across the tropical Pacific from August 30–September 5, 2026, compared to the 1991-2020 average. Compared to the traditional sea surface temperature anomaly (top map), the anomaly relative to the whole tropics (bottom map) tones down the absolute warmth in the key El Niño-monitoring region (black outline), but also makes it more obvious how warm that area is relative to the areas to the west. That cool-to-warm gradient is not normal for the area, and it shifts where rainfall and convection happen. Climate.us maps, based on NOAA OISST data.
Out-of-place rainfall and convection (rising air) got stronger
The classic El Niño atmospheric pattern that was on display in July got even more pronounced in August as the atmosphere reacted to the underlying sea surface temperature anomalies. An image of cloud patterns shows a fat blue bulge of cloudiness straddled the equator in the central Pacific. Meanwhile, the dryness/clear skies over northern Australia and the Maritime Continent deepened.
Grab and drag the slider to compare cloud patterns in July 2026 (left map) to August 2026 (right map.) The iconic cloud pattern associated with El Niño—increased cloudiness and rainfall over the central tropical Pacific (blue) and decreased cloudiness and rainfall over the western Pacific and Maritime Continent (brown)—intensified in August. Climate.us maps based on satellite data of outgoing longwave radiation from University of Maryland.
This symmetry between the ocean temperature anomalies and the cloud/rainfall anomalies is strong evidence that the two parts of the climate system are in lock step and reinforcing each other. The warmer the central Pacific, the more evaporation, rising air (convection), and rainfall there. That isn’t the normal place for the basin’s highest rainfall. What goes up must come down, so that when that rising air hits the top of the troposphere, it spreads out to the west and east, and sinks back toward the surface over over the Maritime Continent and tropical South America. As it sinks, it dries, cutting off clouds and rainfall.
Already bonkers subsurface temperatures got even more bonkers
The final piece of the “100 percent chance” puzzle is what is happening below the surface of the tropical Pacific. This animation shows subsurface temperature anomalies at the equator for 5-day periods from early July to the third week of August. There is so much warm water pooling down there that models and forecasters have zero doubts that the warm anomaly at the surface can be sustained for months.
Five-day average temperature anomalies in the top 300 meters (~1,000 feet) of the equatorial Pacific Ocean from early July through mid-August 2026. (Depth and surface map are not to scale!) Places that are cooler than average are blue; places that were warmer than average are red. Climate.us animation, based on NOAA GODAS data.
This warm water is able to build up because the out-of-place rainfall and rising air motion in the central tropical Pacific weaken the prevailing easterly (from the east) trade winds that usually drive surface waters to the west and force upwelling of cool, deep water in the central and eastern tropical Pacific. Without those winds, upwelling stagnates, allowing the upper ocean to simmer–part of the feedback loop I described above.
[Editor's note: I know that it’s become something of a cliche in climate data visualization to talk about having to re-set the scale (i.e. the temperature range of a map and how it is colored) to accommodate new warmer top-end values, and as a writer, if I can’t do better than cliches, then I might as well cede the field to AI…but I can’t help myself.
This type of graphic, with the flat surface map stitched to the vertical cross section data is something our team started making as we prepared to launch the ENSO blog on Climate[.]gov back in 2014. At the time, a range of plus to minus 5 Celsius (+/- 9 Fahrenheit) was our standard. It already raised our eyebrows last month that we had to widen the scale out to +7.5 ˚C to keep the whole image from blowing out in a big dark red blob. But to prevent that from happening this month, we had to raise the top of the scale AGAIN, this time to +10 ˚C above average. That’s 18 ˚F warmer than average! That’s bonkers! ]
Some of the typical El Niño impacts are starting to emerge
To wrap up our illustrated guide to the September 2026 El Niño outlook, I’ll briefly mention that some of the typical El Niño impacts on climate in the tropics are starting to emerge. El Niño’s suppression of rainfall across Indonesia is showing up in dramatic satellite imagery of fires there.
In addition—and I think Emily is going to talk about this more in her next post—Atlantic hurricane season activity to date is less than 10% of normal according to realtime stats from Colorado State University. The Northeast Pacific is…well I have already used the word bonkers once in this post, so let’s just say unequivocally above average. (In fact, to return to a cliche, does anyone want to place a friendly wager on whether they are going to need to re-scale their plot before the season wraps there?). Both outcomes are typical of El Niño.
And what about some of the other weather and climate extremes that are in the news, like the late summer heat and dryness in the Southern Plains or the heatwaves that have been pummeling Europe this summer? Well…I think what our ENSO experts would tell me to say is something like “There’s little evidence based on past El Niño events to think El Niño is playing a role there.” As Tom DiLiberto put it in a blog post from 2015: you can’t blame everything on El Niño.
Subject matter expert review by Emily Becker.