El Niño 2026-2027 Seasonal Forecast: Spring, Summer, Autumn & Winter Outlook

Published: July 26, 2026 · 9 min read

Current State and Model Consensus

As of July 2026, the equatorial Pacific is firmly in El Niño territory. The Oceanic Niño Index (ONI) — the three-month running mean of SST anomalies in the Niño-3.4 region (5°N-5°S, 120°-170°W) — stood at +0.9°C for the April-June 2026 period, crossing NOAA's El Niño threshold of +0.5°C for the third consecutive season. The most recent weekly Niño-3.4 anomaly, for the week ending July 19, 2026, was +1.2°C, indicating continued warming.

The IRI/CPC model plume, which combines output from 20+ dynamical and statistical models, shows remarkable consensus for this point in the ENSO cycle. Over 90% of ensemble members maintain Niño-3.4 anomalies above +0.5°C through February-March 2027. The dynamical model average peaks at +1.7°C in October-December 2026, while the statistical model average is slightly lower at +1.3°C — a gap that reflects the tendency of statistical models to underestimate strong events. ECMWF's SEAS5 seasonal prediction system, which consistently ranks among the top-performing ENSO forecast models, projects a peak of +1.8°C in November 2026.

Spring 2026: March-May Transition

The March-May 2026 season marked the transition from ENSO-neutral to weak El Niño conditions. The ONI value for MAM 2026 was +0.6°C, barely above the threshold, but the trajectory was more significant than the absolute value. Weekly SST anomalies crossed +0.5°C in mid-April and never dropped back below the threshold — meeting the persistence criterion that separates a temporary warming blip from a real El Niño event.

Spring El Niño transitions produce a distinctive global pattern. In North America, the spring season typically sees a wetter-than-average southern tier and drier conditions in the Pacific Northwest — a pattern that was observed in the March-May 2026 precipitation data, with California receiving 140% of normal rainfall and Oregon-Washington at 60-70% of normal. South America's west coast, particularly Peru and Ecuador, experienced above-average sea surface temperatures and the first hints of enhanced rainfall. The Indian Ocean Dipole was neutral during this period, meaning no amplification or dampening of the El Niño signal from the Indian Ocean basin.

For the East Asian region, spring 2026 brought a mixed pattern. Southern China and Taiwan saw above-average rainfall — consistent with the enhanced subtropical jet that El Niño produces — while the Korean Peninsula and Japan were close to normal. Southeast Asia's pre-monsoon season was drier than average across Thailand, Cambodia, and southern Vietnam, with accumulated rainfall in March-May running at 70-80% of the 1991-2020 normal.

Summer 2026: June-August Intensification

The summer 2026 season is the intensification phase of this El Niño event. SST anomalies in the Niño-3.4 region are projected to reach +1.0 to +1.5°C by August, moving the event from "weak" to "moderate" territory and likely crossing into "strong" (>+1.5°C) by late summer. The June 2026 weekly anomalies already showed +1.2°C by mid-month, suggesting the intensification is proceeding faster than the three-month average implies.

Summer El Niño conditions produce several well-documented teleconnections. The Atlantic hurricane season — which runs June through November — typically sees reduced activity during El Niño summers due to increased vertical wind shear over the tropical Atlantic. NOAA's August 2026 hurricane season update is expected to downgrade the number of named storms from the pre-season outlook of 14-18 to a range of 10-14, with accumulated cyclone energy (ACE) projected at 70-90% of normal. The 2023 El Niño summer produced 20 named storms despite El Niño conditions (due to record-warm Atlantic SSTs offsetting the shear), so this forecast carries more uncertainty than usual.

The Indian summer monsoon (June-September) is negatively correlated with El Niño, and the India Meteorological Department has already projected total rainfall at 92-96% of the long-period average for 2026 — below normal but not catastrophic. The last time a strong El Niño coincided with a severe monsoon deficit was 2015, when June-September rainfall was 86% of normal and kharif (summer) crop production fell 2.5%. The East Asian summer monsoon, which affects China, Korea, and Japan, tends to see a northward shift in the rain belt during El Niño, producing drier conditions in southern China and wetter conditions in the Yangtze-Huaihe basin and northern Japan.

Autumn 2026: September-November Peak

The September-November 2026 season is expected to be the peak of this El Niño event. Model consensus places Niño-3.4 SST anomalies at +1.5 to +2.0°C for this period, with a minority of ensemble members (roughly 20-25% of the CPC/IRI plume) exceeding +2.0°C — the Super El Niño threshold. The RONI (Relative Oceanic Niño Index), which adjusts for the background warming trend in the tropical Pacific, is projected at +1.3 to +1.8°C, reflecting the fact that the absolute SST anomaly overstates the ENSO-related warming component in a warmer baseline climate.

Autumn is the season when El Niño teleconnections are most robust and most damaging. The Pacific Northwest drought signal is historically strongest in SON — the 2015 El Niño produced Seattle's driest September-November on record, with only 2.13 inches of rain compared to a normal of 11.62 inches. California rainfall is typically enhanced during El Niño autumns, but the latitudinal boundary between "drier north" and "wetter south" can shift by 300-500 km depending on the event's exact structure. For 2026, the model consensus places the boundary near the Oregon-California border, delivering above-average precipitation to the Bay Area and Central Valley while leaving Portland and Seattle dry.

The global autumn impacts are extensive. Australia faces elevated drought risk, particularly in eastern Queensland and northern New South Wales, where spring rainfall is already running below normal. The Australian Bureau of Meteorology's seasonal outlook shows a 70% probability of below-median rainfall for eastern Australia during September-November. Southeast Asia's inter-monsoon period (October-November) is projected to be drier than average, compounding the reduced monsoon rainfall from the summer months. Southern Africa enters its rainy season (October-March) with a high probability of below-normal rainfall, and the Famine Early Warning Systems Network has flagged Mozambique, Zimbabwe, and southern Zambia for potential drought conditions.

Winter 2026-27: December-February

The winter 2026-27 season (December through February) will likely see continued strong El Nino conditions, though the event may begin a slow decay from its autumn peak. The classic pattern for North America splits the continent into a warm-and-dry north and a cool-and-wet south. The polar jet stream stays bottled up in Canada, leaving the northern tier with warmer-than-average temperatures — typically +2 to +4F above normal in the Upper Midwest and Great Lakes. The subtropical jet stream, enhanced by El Nino, pumps moisture into the southern US, from California across Texas and the Gulf Coast into Florida.

South America faces the most direct El Nino impacts during austral summer. Coastal warming off Peru and Ecuador — where SST anomalies can exceed +3C in strong events — drives extreme rainfall in the normally arid coastal zone. The 1997-98 El Nino destroyed 50,000 homes and caused $3.5 billion in damage in Peru. Argentina, Uruguay, and southern Brazil tend wetter during El Nino summers, which can benefit soybean and corn production but also elevates flood risk.

Southern Africa's summer drought risk is one of the most consistent ENSO teleconnections, with the region typically receiving 70-85% of normal rainfall during El Nino winters. The 2015-16 El Nino produced a severe drought that left 40 million people facing food insecurity according to the World Food Programme.

The expected decay of this event begins in late winter. By February 2027, Nino 3.4 anomalies remain above +1.0C but cooling signals emerge in the eastern Pacific. The IRI plume shows a 55% probability of neutral conditions by April-June 2027. The spring predictability barrier makes this forecast less reliable — historical events have shown decay timelines ranging from 3 to 8 months after peak. A rapid transition to La Nina by mid-2027 is possible, following the pattern observed after the 1997-98 event.

Spring 2027: Decay and Transition

By March-May 2027, the IRI/CPC forecast shows El Nino probability dropping to 54% and neutral probability rising to 42%. The physical basis for decay is the seasonal cycle: the equatorial cold tongue re-intensifies in spring, the atmosphere-ocean coupling weakens, and the subsurface warm water that has been surfacing in the eastern Pacific since mid-2026 is gradually exhausted.

The historical analogs for a strong event peaking in late 2026 and decaying in early 2027 are instructive but not deterministic. The 1982-83 event decayed by May 1983 and transitioned to La Nina by September 1983. The 1997-98 event decayed by May 1998 and produced a strong La Nina by August. The 2015-16 event decayed by May 2016 and generated a weak La Nina by September. In all three cases, the transition to La Nina occurred within 4-6 months of decay. The 1987-88 and 1991-92 moderate El Ninos, in contrast, decayed gradually and did not transition to La Nina at all — they returned to ENSO-neutral and stayed there for 1-2 years. The key question for 2027 is whether this event follows the strong-event pattern of rapid transition to La Nina (the majority outcome historically, at roughly 70% probability), or whether it settles into an extended neutral period.

For impact assessment purposes, the spring 2027 transition carries reduced but non-zero teleconnection signals. Residual warm SST anomalies in the tropical Pacific continue to exert some influence on global circulation, but this is increasingly modulated by mid-latitude internal variability. Seasonal forecasts for March-May 2027 in key agricultural regions — the US Corn Belt, the Argentine Pampas, the Indian pre-monsoon period — show roughly equal probabilities across terciles (above, near, below normal), reflecting the low signal-to-noise ratio typical of ENSO decay phases. The practical implication is that spring 2027 planting decisions should not rely heavily on ENSO-based seasonal forecasts; other sources of predictability, including soil moisture conditions and multi-model ensemble guidance, become more relevant during decay phases.

Uncertainty Analysis and Model Limitations

While model consensus for El Nino through early 2027 is strong, four specific areas of uncertainty affect the usefulness of this forecast for decision-making. The first is event strength. The IRI plume inter-model spread for the October-December 2026 season ranges from +0.8 to +2.6C across individual model runs. The difference between a moderate El Nino (+1.2C) and a very strong El Nino (+2.2C) matters enormously for impact intensity — the economic damage function for El Nino is nonlinear, with very strong events causing disproportionately larger losses. Callahan and Mankin (2023) in Science found that the 1997-98 and 2015-16 very strong El Ninos each caused roughly $5.7 trillion in global economic losses over five years, while moderate events produced losses 40-60% smaller. If the 2026 event peaks at +1.3C (the low end of the ensemble), its global economic impact will be substantially smaller than if it reaches +2.2C (the high end).

The second uncertainty is the spring predictability barrier — the well-documented decline in ENSO forecast skill for predictions that cross the April-June period. The SPB arises because spring is when the coupled ocean-atmosphere system is least stable: equatorial trade winds are weakest, the thermocline is shallowest, and stochastic atmospheric forcing plays a larger role relative to deterministic ENSO dynamics. For the 2026-2027 forecast, the SPB affects reliability of predictions for mid-to-late 2027. The IRI/CPC estimates that Nino 3.4 forecast skill (anomaly correlation coefficient) drops from roughly 0.85 at a 3-month lead to approximately 0.55 at a 9-month lead crossing the spring barrier. The practical message: forecasts for the March-June 2027 period should be treated as scenarios rather than predictions.

A third uncertainty concerns climate change's influence on ENSO behavior. The IPCC Sixth Assessment Report (2021) concluded with medium confidence that strong El Nino frequency may increase under continued warming. Cai et al. (2019) in Nature found that under RCP 8.5, very strong El Nino frequency could increase from roughly once every 20 years to once every 10 years by 2100, driven by enhanced upper-ocean stratification. Four of the six strongest ONI values since 1950 have occurred since 1982 — this clustering is statistically unlikely under a stationary climate.

The fourth uncertainty involves the possibility of a multi-year El Nino. Roughly 10-15% of historical El Nino events have persisted into a second year — the 2014-16 event is the most recent example. Current models assign a low probability (roughly 15-20%) to El Nino conditions persisting through the second half of 2027. A multi-year event would compound impacts in regions where drought effects accumulate across consecutive dry seasons — Southeast Asia, Australia, Southern Africa. This low-probability but high-consequence scenario warrants inclusion in contingency planning, particularly in agriculture and humanitarian sectors where early action reduces response costs by a factor of 3-7 relative to late intervention, according to analyses by the UN Food and Agriculture Organization and the Start Network.