El Niño 2026-27: How It Works and Why NOAA Calls This One "Historic"

El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO), a natural cycle in which sea surface temperatures in the central and eastern tropical Pacific rise well above average, according to NOAA's education resources. It recurs roughly every two to seven years, NASA notes, and typically peaks between November and January before fading over the following months.

The mechanism: weaker winds, warmer water

In normal, or 'neutral,' conditions, easterly trade winds push warm surface water toward Indonesia, allowing cooler water to well up off South America. This east-west temperature contrast drives the Walker Circulation, an atmospheric loop that rises over the warm western Pacific and sinks over the cooler eastern Pacific, as described by NOAA's climate education materials.

During El Niño, those trade winds weaken or reverse. Warm water that would normally pile up near Asia instead spreads east across the Pacific, and upwelling of cold, nutrient-rich water off Peru and Ecuador slows or stops, per NASA's Earth science explainer. The Walker Circulation cell weakens and shifts eastward, which in turn moves the location of rising tropical rainfall and alters the path of the jet stream over North America.

Why this event is being called a 'super' El Niño

NOAA's Climate Prediction Center said in its October 8, 2026 ENSO diagnostic discussion that sea surface temperature anomalies exceeded +4.0°C in parts of the eastern equatorial Pacific, with the benchmark Niño-3.4 index at +2.1°C. FOX Weather reported that Pacific water temperatures in the central equatorial Pacific averaged more than 2°C above normal in September 2026, a level NOAA considers 'Super El Niño territory.'

CPC forecasters put the probability that this event will exceed the historic +2.5°C threshold at 54% for September-November, 83% for October-December, and 70% for November-January — a threshold that, if crossed, would make it the strongest El Niño on record dating back to 1950. The same October 8 discussion put the chance of El Niño conditions persisting through January-March 2027 at more than 83%.

NOAA's U.S. winter outlook

NOAA released its official 2026-27 Winter Outlook on October 15, 2026, forecasting a 'very strong El Niño' influence on the December-February season. The agency expects warmer-than-average temperatures across northern California, the Pacific Northwest, the Midwest, the Mississippi Valley, much of the East, Alaska, and Puerto Rico and the U.S. Virgin Islands. Near-normal temperatures are favored for parts of the Southeast, including Florida, while Hawaii and much of the Southwest fall into the 'equal chances' category, meaning no strong tilt either way.

On precipitation, NOAA favors wetter-than-average conditions across the southern tier — from the Southwest through the Southeast — and along the East Coast. Drier-than-average conditions are favored for Hawaii, much of Alaska, the northern Mountain West, and parts of the Great Lakes.

NOAA projects drought improvement or resolution across the Southwest, Southern Great Plains, Southeast and East Coast, but expects drought to worsen in the northern Rockies, northeastern Oregon and eastern Washington. FOX Weather's reporting added that increased precipitation could help ease long-running drought in the Southwest and Southern Plains, while noting that NOAA's Graham warned heavy rain falling on already dry soil can trigger flash floods and mudslides.

Effects reach far beyond the United States

El Niño's influence is not confined to North America. NASA's Earth science explainer describes global ripple effects: flooding in normally arid parts of South America alongside drought in the Amazon, monsoon failures and wildfire-inducing dry spells in Indonesia and India, drought in northern Australia, and severe drought across southern Africa. NASA cites the 2015-16 El Niño as displacing more than 150,000 people in Uruguay, Paraguay and Argentina, and notes the United Nations reported in April 2016 that roughly 60 million people across Africa, Asia, the Pacific and Latin America needed food assistance due to weather extremes linked to that event.

The same NASA source notes El Niño years tend to rank among the hottest on record globally, since heat stored in the Pacific Ocean is released into the atmosphere, and the event is also linked to suppressed Atlantic hurricane activity, worldwide coral bleaching, and disruption of marine fisheries.

What's known and what remains uncertain

The ENSO index values and probability percentages come directly from NOAA's Climate Prediction Center, which updates its diagnostic discussion monthly. CPC's own outlook stresses that strength categories are probabilistic, not certain: an 83% chance for October-December does not rule out the event falling short of the historic +2.5°C threshold. NOAA's winter outlook also measures probability, not certainty, over three-month temperature and precipitation categories, meaning any individual storm, cold snap, or local deviation remains possible within a season that is statistically tilted toward the patterns described above.