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How strong is the 2026–27 El Niño—and what could it mean for winter weather?
NOAA gives a 70% chance that El Niño reaches a three month Relative Oceanic Niño Index of at least +2.5°C in November–January, a level associated with a historic strength event. All 51 runs of a seasonal model forecast wetter than normal December–March conditions for San Francisco, averaging about 26 inches—nearly t...
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Key takeaways
- NOAA gives a 70% chance that El Niño reaches a three month Relative Oceanic Niño Index of at least +2.5°C in November–January, a level associated with a historic strength event.
- All 51 runs of a seasonal model forecast wetter than normal December–March conditions for San Francisco, averaging about 26 inches—nearly twice normal—but seasonal outlooks cannot pinpoint individual storms.[35][44]
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openai.comCreate a landscape editorial hero image for this Studio Global article: How strong is the 2026–2027 El Niño and what are its expected regional impacts, including how Meteored’s NOAA-based August–October relative. Article summary: The available evidence supports a strengthening, potentially historic 2026–2027 El Niño, with NOAA expecting strong-to-very-strong conditions through January–March 2027 at greater than 83% probability.[4] However, the re. Topic tags: general, government, education, general web. Style: premium digital editorial illustration, source-backed research mood, clean composition, high detail, modern web publication hero. Use reference image context only for broad subject, composition, and topical grounding; do not copy the exact image. Avoid: logos, brand marks, copyrighted characters, real person likenesses, fake screenshots, UI text, readable text, watermarks, charts w
The 2026–27 El Niño is strengthening, and NOAA’s October outlook puts the event in record-strength territory. Its probabilities vary by season, while forecasts for the United States and western Pacific point to differing regional risks. These outlooks describe chances and broad patterns, not a precise forecast of weather in any one place.
How strong is the event?
Meteored reports that the August–October three-month relative anomaly reached +2.0°C, which it describes as “very strong” under NOAA’s operational criteria.24 NOAA’s October outlook separately assigns a 70% chance that the November–January three-month Relative Oceanic Niño Index (RONI) will reach +2.5°C or higher, a level NOAA associates with an event exceeding previous El Niños in records dating back to 1950.
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Those figures refer to different overlapping three-month periods. NOAA’s outlook gives a 54% probability for September–November and 83% for October–December at the same +2.5°C RONI threshold.2 NOAA also says strong-to-very-strong conditions are likely through January–March 2027, with the probability remaining above 83%.
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The odds describe an evolving forecast, not a certainty that the event will set a record. NOAA’s outlook synthesizes multiple models, and the agency describes the coupled ocean–atmosphere system as strengthening.2
RONI and ONI measure the warming differently
The conventional Oceanic Niño Index (ONI) tracks sea-surface-temperature anomalies in the Niño 3.4 region. RONI adjusts the regional anomaly in relation to broader tropical-ocean temperatures, helping distinguish Pacific warming from the background warmth across the tropics.8
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That distinction matters when comparing headline numbers: an ONI value and a RONI value are not interchangeable. One available summary of the traditional Niño 3.4 index reports a July–September seasonal mean of +2.46°C; NOAA’s relative-index reporting cited by Climate.gov gives a July–September RONI value of +1.7°C.6
12 The supplied NOAA material does not confirm the proposed +2.2°C and +2.5°C ONI readings for the later seasons, or the claimed February 2026 introduction date for RONI, so those details should not be treated as established here.
The World Meteorological Organization’s forecast is another measure: it says tropical Pacific sea-surface temperatures could reach 3.8°C above average during November 2026–January 2027.11 WMO has described the event as likely to peak toward the end of 2026.
14 That +3.8°C forecast should not be converted directly into a RONI value: the supplied sources do not provide an official WMO RONI equivalent.
What U.S. forecasts suggest
California: a wet signal for San Francisco, not a storm-by-storm prediction
All 51 runs of a seasonal model forecast wetter-than-normal conditions in the San Francisco area from December through March. Their average is about 26 inches of rain, nearly twice normal, according to the San Francisco Chronicle.35 The ensemble result signals a strong wet-season outlook; it does not mean each run predicts the same total or that every storm will bring heavy rain.
NOAA’s broader December–February outlook favors wetter-than-average conditions across the southern United States, from California to Florida, and warmer-than-average conditions across the northern United States.1 For Northern California, San Francisco’s severe-storm preparedness page also reports a wetter-than-normal outlook for December through February.
44 But a strong El Niño does not determine when individual storms arrive, where they hit, or how severe they become.
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Coastal-water temperature claims need more evidence
Specific claims that California coastal waters will reach 10–13°F above normal, or about 67°F near San Francisco rather than 54°F, are not confirmed by the provided NOAA or WMO source excerpts. Without a verifiable forecast for those figures, they cannot establish how much extra moisture storms might carry.
Western Pacific drying and humanitarian concerns
The WMO Pacific Regional Climate Centre Network expects below-normal rainfall from November 2026 to January 2027 across parts of the western and southwestern Pacific, including areas from Palau to the Marshall Islands and from central and southern Papua New Guinea to southern French Polynesia. The WMO says this could raise water-supply concerns in places already experiencing low rainfall.9
WMO Secretary-General Celeste Saulo has warned that the event could be unprecedented in strength and that its effects may continue beyond its late-2026 peak. She has also called for decisive action to protect vulnerable communities.18
20 Those warnings underline why seasonal outlooks matter for preparedness, while not establishing a specific outcome for every region.
The practical takeaway
The strongest supported conclusion is that NOAA sees substantial odds of a historic-strength El Niño through the coming winter, while seasonal forecasts signal a wetter winter for parts of the southern United States and a drier one for parts of the western Pacific.1
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9 The San Francisco model ensemble is notably wet, but neither an ocean index nor a seasonal average can guarantee local rainfall totals or predict individual storms.
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NOAA gives a 70% chance that El Niño reaches a three month Relative Oceanic Niño Index of at least +2.5°C in November–January, a level associated with a historic strength event.
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NOAA gives a 70% chance that El Niño reaches a three month Relative Oceanic Niño Index of at least +2.5°C in November–January, a level associated with a historic strength event. All 51 runs of a seasonal model forecast wetter than normal December–March conditions for San Francisco, averaging about 26 inches—nearly twice normal—but seasonal outlooks cannot pinpoint individual storms.[35][44]
Sources
meteored.com.arEl Niño alcanza la categoría de "muy fuerte" y la Organización Meteorológica Mundial prevé un pico de +3,8 °C
cpc.ncep.noaa.govClimate Prediction Center: ENSO Diagnostic Discussion
coralreefwatch.noaa.govENSO Conditions and Coral Bleaching
weather.comSuper El Niño nears a record, and the weather looks like it