Full Breakdown
Forecast of a Potentially Historic El Niño for Winter 2026-27
8/18/2026, 11:36:10 AM
The Emerging Event
The U.S. Climate Prediction Center (CPC) has raised the probability of a very strong El Niño during October – December 2026 to 95 %, up from 81 % in July. The August outlook also gives a 90 % chance for a very strong event in November – January and 70 % for December – February. The median forecast for October-December places the Relative Oceanic Niño Index (RONI) at +2.66 °C (+4.8 °F), with an inter-quartile range of +2.37 °C to +2.95 °C.
Background & Context
El Niño, the warm phase of ENSO, is driven by anomalously warm sea-surface temperatures (SSTs) in the central-eastern equatorial Pacific. In July 2026, NOAA’s CPC recorded SST anomalies of +1.4 °C in Niño-3.4, +1.7 °C in Niño-3, and +2.9 °C in Niño-1+2, alongside weakened easterly trade winds and enhanced westerly wind bursts. Downwelling Kelvin waves that began in December 2025 and recurred through June 2026 have deepened the thermocline, allowing subsurface heat to spread eastward.
Timeline
- July 16 2026: CPC issued its seasonal outlook before the August update.
- August 13 2026: ENSO Diagnostic Discussion to be released by CPC.
- August 20 2026: CPC will issue its next long-lead U.S. seasonal outlook with updated probabilities.
Data & Statistics
- SST anomalies: Niño-3.4 +1.4 °C; Niño-3 +1.7 °C; Niño-1+2 +2.9 °C (CPC, July 2026).
- RONI median: +2.66 °C (Oct-Dec); +2.23 °C (Dec-Feb) (CPC, August 2026).
- Very strong event probability: 95 % (Oct-Dec), 90 % (Nov-Jan), 70 % (Dec-Feb) (CPC, August 2026).
- Australian BoM: Niño-3.4 +2.20 °C for week ending Aug 9; July Southern Oscillation Index –29.1 (most negative July on record).
- JMA: Niño-3 +2.5 °C for July, tying the 1997 record.
Why It Matters
A very strong El Niño reshapes North American weather. CPC projects wetter-than-normal conditions across the southern tier and drier-than-normal conditions across the Northwest and northern Plains for winter. Above-normal temperatures are favored across the West, the northern tier, and parts of the East. In Canada, the outlook suggests warmer northern regions and higher snowfall in the southeast, though predictability remains limited.
Globally, El Niño nudges average temperatures upward and raises drought risk in East Africa, crop-failure risk in Ethiopia and Kenya, and reduces rainfall in Panama’s Canal watershed. It also tends to suppress Atlantic hurricanes while enhancing Eastern-Pacific storms.
Official Statements & Responses
- Australian BoM noted July’s equatorial upper-ocean heat anomaly was the highest on record since its 1979 dataset began.
Conflicting Reports & Gaps
- Probability estimates differ: NOAA’s CPC cites a 95 % chance for Oct-Dec, while ABC News reports a 69 % chance the event will exceed the strength of all previous El Niños since 1950.
- Index comparability: CPC, BoM, and JMA use different regions and calculations, making direct numerical comparison inappropriate.
- Impact uncertainty: CPC acknowledges a “broad spread among ensemble members,” indicating less extreme outcomes remain possible.
What’s Next
- August 20 2026: CPC will release its next U.S. seasonal outlook with the latest probabilities.
- August 13 2026: The ENSO Diagnostic Discussion will detail the oceanic and atmospheric drivers.
These products will refine expectations for winter 2026-27 and guide preparedness actions across agriculture, water management, and disaster-risk agencies.
