A historic El Niño is now in play. Here’s what NOAA’s new forecast means for the U.S. winter.
The tropical Pacific has moved from “strong” to an unusually confident forecast for “very strong.” That raises the odds of recognizable U.S. winter patterns—but it does not turn a seasonal signal into a local weather guarantee.
The most important line in NOAA’s September El Niño update is not that a warm patch of Pacific water has become warmer. It is that the ocean and atmosphere are now behaving together in a way that makes a powerful event increasingly difficult to dismiss as a model-only possibility.
On September 10, the National Weather Service’s Climate Prediction Center said El Niño was strengthening and put the chance of a very strong event during Northern Hemisphere fall and winter 2026–27 above 90%. For October through December, forecasters assigned a 75% chance that the three-month Relative Oceanic Niño Index, or RONI, would reach at least +2.5°C—a level NOAA described as strong enough to exceed previous El Niño events in its record dating to 1950.
That is an unusually emphatic seasonal signal. But it is also easy to misread. A record-scale El Niño does not mean every city gets record rain, every mountain gets record snow, or every northern state has a mild winter. El Niño changes the background circulation of the atmosphere. It tilts odds. It changes which storm tracks are favored and which regions are more likely to end a season wetter, drier, warmer or cooler than normal. Daily weather still depends on shorter-lived patterns that cannot be resolved months in advance.
What changed: the Pacific is no longer sending a mixed signal
In August, the Niño‑3.4 index—the closely watched region of the east-central equatorial Pacific—rose to +1.8°C, up from +1.4°C in July. NOAA also measured +2.5°C in Niño‑3 and +3.4°C in the far-eastern Niño‑1+2 region. Parts of the eastern equatorial Pacific were more than 3°C above average at the surface, while exceptionally warm water persisted below the surface as well.
Those numbers matter because El Niño is not defined by sea-surface temperature alone. Forecasters look for an atmospheric response: weaker or reversed trade-wind anomalies, changes in high-altitude winds, shifts in tropical rainfall, and pressure patterns consistent with the warm water underneath. NOAA’s September discussion reported stronger rainfall and convection from the central to eastern Pacific, suppressed rainfall over Indonesia, and wind anomalies stretching across much of the equatorial basin. In plain English, the atmosphere is increasingly acting like it “believes” the warm ocean.
That coupling is what allows a disturbance thousands of miles from Chicago, Atlanta or Sacramento to influence the winter jet stream over North America. Tropical thunderstorms release enormous amounts of heat high into the atmosphere. When the main zone of those storms shifts eastward during El Niño, it reorganizes planetary-scale circulation. The result is not a single storm path but a persistent nudge to the atmosphere over weeks and months.
A stronger El Niño makes the classic pattern more useful—but never certain
The advantage of a strong El Niño is not that it lets meteorologists predict January weather in September. It improves the odds that the broad winter pattern will resemble what has happened during other El Niño years. NOAA’s climate scientists have repeatedly emphasized that the stronger the event, the more likely the United States is to show a recognizable El Niño precipitation pattern. “More likely,” however, is the critical phrase.
Past strong events do not line up perfectly. California can be dramatically wet in one major El Niño and surprisingly ordinary in another. Snowfall can rise in a region even if seasonal temperatures are above normal, provided storms and cold air overlap at the right times. A warmer Northeast can still have a major blizzard. A wetter Southeast can still experience long dry stretches between storm systems.
Seasonal climate guidance is most useful as a risk map: it tells planners where the odds have moved, not what the weather will be on a particular Tuesday.
That distinction becomes more important when a headline says “historic.” The 2026 event may compete with or surpass the largest El Niños in the modern observational record. But a historic ocean index and a historic local impact are different questions. Local outcomes also depend on the exact placement of tropical heating, North Pacific sea temperatures, Arctic variability, the Madden-Julian Oscillation and shorter atmospheric waves that can temporarily reinforce or oppose the larger El Niño tendency.
Where the U.S. signal is strongest
Historically, the clearest cold-season El Niño signal in the contiguous United States is increased precipitation along the Gulf Coast and much of the Southeast. NOAA’s long-running composites show that the Pacific jet stream tends to strengthen and shift south, sending more storm systems across the southern tier. The Southeast has been one of the more consistent places to see above-normal winter precipitation during strong events.
California also gets intense attention because strong El Niños can aim more Pacific storms toward the state. That can improve reservoir inflows and mountain snowpack, but it can also raise the risk of flooding, debris flows and coastal damage. The state’s record is a warning against simple formulas: some famous strong El Niños brought exceptional rain, while others failed to deliver the statewide deluge people expected. The location and timing of atmospheric rivers still matter.
Farther north, the Pacific Northwest and northern tier of the country often lean warmer, and parts of the Northwest, northern Rockies, Ohio Valley or Upper Midwest can lean drier depending on the season and the exact event. NOAA’s August long-lead outlook already used the developing El Niño as a major input, favoring above-normal temperatures across broad northern and western areas while showing the precipitation pattern becoming progressively more El Niño-like into winter.
Wet odds rise
The cold-season wet signal is among the most reliable U.S. El Niño relationships, which can elevate river, flash-flood and severe-weather planning concerns.
More storm opportunities
A stronger southern jet can increase the number of moisture-bearing systems, but the exact landfall corridor and snow level determine whether water supply or flood risk dominates.
Milder tilt, with caveats
Warmer conditions become more likely in many northern areas, yet individual Arctic outbreaks and heavy snow events remain entirely possible.
California’s question is not simply “wet or dry?”
For California water managers, the useful questions are more granular. Will storms arrive as a series of moderate systems or cluster into a few high-impact atmospheric rivers? Will Sierra Nevada temperatures be cold enough to store precipitation as snow, or will more of it fall as rain and run quickly into rivers? Will major storms arrive after burn scars have had time to recover, or when soils are already saturated?
El Niño can raise the probability of a wetter winter, especially across the southern part of the state, yet reservoir operations have to balance flood-control space against water storage. A stormy winter can refill surface supplies and improve snowpack while simultaneously creating emergency-management problems. A warm storm can also produce much more runoff than a cold one. Seasonal guidance therefore influences preparation, but short-range forecasts still drive gate operations, evacuation warnings and road closures.
One practical consequence is that communities do not need to know whether the coming winter will be “record wet” to justify maintenance now. Clearing drainage systems, inspecting culverts, reviewing debris-flow zones and checking flood-control equipment are low-regret moves when the seasonal odds shift toward more southern storm activity.
The Pacific Northwest may lean milder—and that can reshape snow and energy demand
El Niño winters often favor warmer conditions in the Pacific Northwest and parts of the northern United States. That can reduce heating demand during long stretches, but it can also raise snow levels in mountain watersheds. A winter with normal total precipitation can still produce less snow storage if more storms arrive warm. That matters for spring runoff, hydropower planning, recreation and ecosystems that depend on cool-season snowpack.
The Northwest’s dry signal is less reliable than the Southeast’s wet signal, which is another reason not to convert the broad pattern into a local deterministic forecast. A few strong Pacific storms can erase a seasonal deficit quickly. Conversely, a warm winter can produce damaging rain-on-snow events even if total precipitation does not rank as extreme.
The hurricane-season connection is already visible
El Niño’s reach is not limited to winter. In August, NOAA updated its 2026 Atlantic hurricane outlook to give a 75% chance of a below-normal season, with 7 to 13 named storms, 2 to 6 hurricanes and 0 to 2 major hurricanes in the full season range. The agency explicitly cited the strengthening El Niño as a major reason: upper-level winds associated with El Niño tend to increase vertical wind shear over the tropical Atlantic, making it harder for developing storms to organize.
That is good news at the basin scale, but it is not a landfall forecast. A quiet season can still produce a devastating hurricane if one storm reaches a vulnerable coast. El Niño changes the number and favorability of storms; it does not create a protective shield over Florida, Texas, Louisiana or the East Coast.
The ocean impact does not stop at the shoreline
NOAA fisheries scientists are also tracking the 2026–27 El Niño as a marine event. Warm anomalies can move northward along the West Coast and interact with existing marine heatwaves. That can reorganize where plankton, forage fish, squid and larger predators are found. Species that prefer cooler water may retreat north or deeper, while warm-water species can appear far outside their usual range.
These shifts matter economically because commercial and recreational fisheries are built around assumptions about where species will be available, when migration will occur and how much food is present at each level of the food web. They also matter ecologically. Marine mammals and seabirds can struggle when prey shifts away from traditional feeding grounds, and warm water can reduce nutrient-rich upwelling in some areas.
What scientists will watch next
The September update increases confidence in the big picture, but several pieces will determine how the U.S. experiences the event. Forecasters will watch whether the Niño‑3.4 region continues to warm toward the predicted peak, whether the atmosphere remains tightly coupled to the ocean signal, and whether the warmest water remains concentrated farther east or broadens westward. Those details can alter where the strongest teleconnections emerge.
They will also watch shorter climate patterns that can temporarily reshape the jet stream. The Madden-Julian Oscillation can amplify or disrupt tropical convection on timescales of weeks. Arctic and North Atlantic circulation patterns can decide whether cold air is available when a storm reaches the East Coast. North Pacific sea-surface temperatures can reinforce or offset parts of the canonical El Niño pattern.
The next decision points
For cities, utilities and households, the forecast is a reason to prepare—not panic
Seasonal climate information is valuable precisely because it arrives before a specific storm exists. Public works departments can clean storm drains and inspect culverts. Water agencies can review flood-control curves and emergency communication plans. Utilities can stress-test assumptions about heating demand, mountain snowpack and hydropower. Farmers can revisit drainage, irrigation and planting contingencies. Insurers and property managers can focus inspections on roofs, trees, sump systems and known flood pathways.
- Flood-prone neighborhoodsClear drainage paths, understand local warning systems and verify insurance coverage before the wettest months.
- Mountain communitiesPlan for both heavy snow episodes and warm rain events; El Niño does not guarantee one snow regime.
- Water agenciesPrepare for volatility: a wetter seasonal tilt can produce both storage gains and high-runoff emergencies.
- Businesses & logisticsReview winter-route alternatives, backup power and supplier exposure in regions vulnerable to flooding or storm disruption.
What not to do with this forecast
- Do not assume “historic El Niño” means your city will have a historic winter.
- Do not treat a seasonal wet signal as a substitute for flood or evacuation alerts issued during an actual storm.
- Do not assume a mild seasonal temperature outlook eliminates freezes, blizzards or Arctic outbreaks.
- Do not use basin-wide hurricane suppression as evidence that coastal preparation is unnecessary.
The signal is unusually loud. The weather will still be local.
The September forecast marks an important shift in confidence. Early in the year, forecasters were still asking whether El Niño would form and how strong it might become. By September, the discussion had moved to whether the event would reach the top of the historical scale. The Pacific’s surface warmth, deep heat reservoir, winds and tropical rainfall are now pointing in the same direction.
For the United States, that increases confidence in the broad physics: a more active southern storm corridor, a wetter tilt across parts of the South, and warmer or drier tendencies across portions of the northern tier. It also supports NOAA’s expectation of a quieter Atlantic hurricane season. Along the West Coast, the event could affect marine ecosystems as well as rain and snow.
But the best way to use the forecast is not to ask whether El Niño guarantees a flood, a snow drought or a warm Christmas. It is to ask which risks have become more plausible and whether preparations can be improved before winter. NOAA’s message is unusually strong about the ocean pattern. It is deliberately cautious about the local outcome. Both parts deserve equal weight.
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