The warm phase of the Pacific is running second only to 1997 and is forecast to set a new record by late fall. Here is where it stands, what the models expect, how it rearranges the winter jet stream, and why a record El Niño is still not a guaranteed record winter.
The 2026-27 El Niño is on track to be the strongest since reliable records began in 1950. NOAA's Climate Prediction Center has an El Niño Advisory in effect, puts the chance of a "very strong" event this fall and winter above 90%, and gives a 75% chance that the October–December average will pass +2.5°C on its official index — beyond anything measured since 1950. Sea-surface temperatures in the eastern equatorial Pacific are more than 3°C above normal.
That much is not in dispute. What is less settled, and what matters more for anyone planning a winter, is what a record-strength El Niño will actually do to weather in North America. The answer depends on the jet stream, on a few other ocean patterns that are not cooperating this year, and on luck. This article walks through all of it, using NOAA and international forecast data alongside DisasterAWARE's own hazard archive. We will update it each month as the event develops.
The numbers, as of the latest official updates:
One detail is easy to miss: this El Niño began from the opposite state. At the start of 2026 the Pacific was in weak La Niña conditions, with RONI at −0.91°C for December–February. The swing of more than 2°C in about six months is part of what makes this event unusual.
The chart below compares 2026 with four big El Niños that are the usual reference points — 1972-73, 1982-83, 1997-98 and 2015-16 — and with 2023-24, the most recent. It lines each of them up from January of its onset year, on NOAA's official index, with NOAA's September forecast for 2026 shown as a shaded band.
At the same point in the calendar, June–August, only 1997 was stronger (+1.50°C against 2026's +1.36°C). 2026 is ahead of 2015 (+1.27), 1972 (+1.14), 1982 (+0.89) and 2023 (+0.54). The record for any three-month period since 1950 is +2.40°C, set in December–February 1982-83; 1997-98 peaked at +2.28 and 2015-16 at +2.25.
CPC's median forecast has 2026 peaking at +2.67°C in October–December — about a quarter of a degree above the 1982-83 record — before fading through the spring.
If you have seen headlines saying this El Niño has already broken records, and others saying it is merely near them, both can be right. They are using different yardsticks.
The traditional Niño-3.4 index measures how much warmer that patch of Pacific is than its long-term average. On that measure, 2026 is first by a wide margin: its August value of +2.52°C compares with +1.68°C in 1997 and +1.65°C in 2015, and its latest weekly reading has reached +3.0°C.
The relative index, which NOAA adopted as its official measure on February 1, 2026, subtracts the average warming of the entire tropical ocean before comparing. The reasoning is physical: what drives El Niño's effects on weather is how much warmer the central Pacific is than the rest of the tropics, because that contrast is what shifts where tropical storms form and where the atmosphere is heated. As Emily Becker of the ENSO Blog put it, "when the Niño-3.4 region is warmer than average, but the rest of the tropics are also warmer than average, the El Niño-related atmospheric response is muted." The whole tropical ocean is unusually warm this year, so the relative index reads roughly 0.7–0.9°C lower than the traditional one.
The practical lesson comes from 2023-24. On the traditional index it looked like a "very strong" event, peaking at +2.0°C. On the relative index it peaked at only +1.42°C, a moderate event — which matches the weaker-than-expected effects it actually had. This article uses the relative index unless it says otherwise.
Every major forecast system expects a very strong event. They differ on how strong.
The 24 models on IRI's September plume peak between +2.34°C and +4.66°C on the traditional index, with a median of +3.45°C; 18 of the 24 exceed +3.0°C. Physics-based models run somewhat warmer than statistical ones. The World Meteorological Organization's multi-model average is about +3.6°C for September–November.
Two cautions belong next to these numbers. No seasonal forecast system has ever been tested against an event this large, so the upper end of the range is genuinely uncertain. And model strength is not the same as impact strength. The WMO says it plainly: "the strength of an El Niño event does not translate directly into the magnitude of impacts in any region."
El Niño's influence on North American weather travels through the jet stream — the fast river of air, several miles up, that steers storms.
The chain runs like this. The unusually warm central and eastern Pacific heats the air above it and fuels towering thunderstorms. That extra tropical heating strengthens the flow of air toward the poles, which in turn strengthens and lengthens the subtropical jet stream — the southern of the two main jets. In a typical winter it fades out over the middle of the Pacific. In a strong El Niño winter it can reach all the way across to California and the Gulf Coast.
NOAA's Climate Prediction Center describes four typical changes in an El Niño winter:
A deeper, eastward-shifted low-pressure area in the Gulf of Alaska — the Aleutian Low — is part of the same pattern. The combined result is more rain and snow across California, the Southwest and the Gulf Coast, and a milder, less stormy winter across the northern United States and western Canada. The Pacific Northwest and northern Rockies tend to get fewer storms, and the storms they do get arrive with milder Pacific air — which is where the rain-versus-snow problem for skiers comes from.
NOAA's seasonal outlook, issued September 17, follows that pattern closely.
For December–February:
These are probabilities, not predictions of totals. A 60% chance of a wetter-than-normal winter still leaves a 40% chance of something else.
This is the part of the story most coverage skips, and it is the part that matters most for planning.
The last "Godzilla" El Niño missed its biggest target. 1982-83 and 1997-98 both brought 150% or more of normal precipitation to California. The 2015-16 event, which was comparably strong, delivered totals below the average for non-El Niño years, according to research from Scripps Institution of Oceanography. The explanation researchers settled on: record warmth in the Indian Ocean and western Pacific pushed the storm track north, sending the rain that should have hit California into the Pacific Northwest instead.
The ocean background is different this time. NOAA's own September outlook flags it directly. The three biggest El Niños since 1950 — 1982-83, 1997-98 and 2015-16 — all coincided with a positive phase of the Pacific Decadal Oscillation (PDO), a slower pattern of North Pacific ocean temperatures that reinforces El Niño's effects. This year the PDO is strongly negative, at −1.11 in August, which CPC says "may dampen the typical impacts of a strong El Niño in certain areas." Warm water in the Gulf of Alaska has also shifted west, which could let slightly cooler water influence parts of the West Coast.
Atmospheric rivers decide California's winter, and they cannot be forecast a season ahead. Most of California's major floods come from atmospheric rivers — long, narrow plumes of tropical moisture — and they arrive in El Niño years and non-El Niño years alike. Alexander Gershunov of Scripps puts it memorably: "Atmospheric rivers are the agents of ENSO heresy in California."
Short-term patterns can override the seasonal one. The Madden-Julian Oscillation, a pulse of tropical storminess that circles the globe every 30 to 60 days, can open the door to an Arctic outbreak or a warm spell for weeks at a time, whatever El Niño is doing.
The National Weather Service's own warning record gives a direct way to test the "El Niño means California floods" assumption. The chart below counts every flood, flash flood and river flood warning the Weather Service issued for California between November and March, for every winter since 2007-08, colored by that winter's El Niño or La Niña phase.
The result cuts against the popular story. The two biggest flood-warning winters in California were both La Niña years: 2016-17, with 355 warnings, and 2022-23, with 238. The two strong El Niño winters in the record were unremarkable — 45 warnings in 2009-10 and 61 in 2015-16, the median of all 19 winters. The last El Niño, 2023-24, came in at 93, exactly the same as the La Niña winter that followed it.
A warning is not a flood, and a single storm can produce dozens of warnings across several Weather Service offices. But the count is a consistent yardstick: the same forecasters, the same rules, every winter. By that yardstick, California's big flood winters have not depended on El Niño.
None of this means California will stay dry. NOAA's outlook favors a wet winter there, and a strong El Niño raises the odds. It means the odds are all you get.
For skiers, El Niño is a story of winners and losers, and the dividing line runs roughly through the middle of the West. We looked at April 1 snowpack in every strong El Niño winter since 1972 at stations near major ski areas. The Pacific Northwest came in below normal in almost every one; Arizona and New Mexico usually did very well; Utah and Colorado showed almost no signal either way; and the Sierra ranged from drought to historic, with big years in half of them. Even the best regions had a bad year when a strong start melted out in a warm February.
That analysis, region by region, is in our companion piece: El Niño and the 2026-27 Ski Season: Which Mountains Tend to Win, and Which Lose.
El Niño's effects on the rest of the world are further along than its effects on North American winter — in several places they are under way now.
We will update this article after each NOAA update through the winter, adding what DisasterAWARE's alerting records as the season unfolds.
Test the El Niño story against what actually happened
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Is the 2026-27 El Niño going to be the strongest on record? Probably. NOAA gives a 75% chance that its official October–December index will reach +2.5°C or more, which would beat every El Niño since 1950. The current record on that index is +2.40°C, from 1982-83. On the traditional index, 2026's weekly readings have already passed those of 1997 and 2015 at the same point in the year.
What is the difference between ONI and RONI? The Oceanic Niño Index (ONI) measures how warm the central-eastern Pacific is compared with its long-term average. The Relative ONI (RONI), NOAA's official index since February 2026, compares it with the rest of the tropical ocean instead. Because the whole tropics are unusually warm, RONI currently reads about 0.7–0.9°C lower than the traditional measure, and it tracks El Niño's weather effects more closely.
Does El Niño mean a wet winter in California? It raises the odds but does not guarantee it. NOAA's outlook gives 50–60% odds of a wetter-than-normal December–February along the California coast. But the 2015-16 El Niño, comparable in strength, left California drier than an average non-El Niño year, and the Weather Service's own warning record shows California's biggest flood-warning winters came in La Niña years.
How does El Niño affect the jet stream? Extra heating over the warm equatorial Pacific strengthens and lengthens the subtropical jet stream, which can reach across to California and the Gulf Coast. The storm track shifts south, bringing more storms to the southern United States and a milder, drier winter to the northern tier and western Canada.
When will El Niño end? NOAA's forecast has it peaking in October–December 2026, weakening quickly through early 2027, and most likely weak or neutral by April–June 2027.
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