El Niño 2026 seasonal outlook: What to expect for Chile?

The ECMWF SEAS5 seasonal forecast issued in May projects a consolidating El Niño through the second half of 2026, with sea surface temperature (SST) anomalies exceeding +2 °C by October. For Chile, the signal matches the classic fingerprint: warmer winter and spring in the north and the Andes, and above-average precipitation in south-central Chile from August onward.

What El Niño is — and why it matters

The El Niño–Southern Oscillation (ENSO) is the dominant source of interannual climate variability over the tropical Pacific. It manifests as anomalous SST warming in an ocean stripe —the Niño 3.4 region— that shifts global atmospheric circulation and reshapes rainfall, temperature and storm patterns far from the tropics.

Chile is especially responsive. During El Niño events central Chile tends to see wetter winters and the cordillera often accumulates more snow than usual, translating into greater water availability for the following agricultural season and hydro generation. Conversely, northern Chile and the altiplano often face drier summers and stronger heatwaves.

The operational implication is direct: anticipating the ENSO phase lets you reposition planning choices months ahead —irrigation schedules, reservoir policy, wildfire preparedness, logistics sizing — in sectors where the gap between wet and dry outcomes is measured in very large sums.

Niño 3.4 index — How the outlook evolves

The Niño 3.4 index is the SST anomaly averaged over 5°N–5°S, 170°W–120°W. SST held above +0.5 °C for five consecutive months formally defines El Niño; sustained values below –0.5 °C denote La Niña; between those thresholds lies neutral ENSO.

SEAS5’s trajectory implies monotonic intensification: it opens at the bottom of the El Niño regime (+0.5 °C) in May, reaches about +1 °C by June and exceeds +2 °C by October. The signal is robust —the model shows no reversal or regime flip in the analysed window— and consistent with a mature phase likely centred on austral summer 2026/27.

Impacts across Chile — Monthly mean temperature

Two-metre temperature anomalies show a broad, persistent warm signal from May to October that strengthens as El Niño matures. The largest departures concentrate along the cordillera and the northern-central foothills and may locally exceed +2 °C.

Operationally, a hotter spring cordillera has three tangible consequences: (1) earlier snowmelt, compressing the hydrological replenishment window and forcing demand rescheduling; (2) higher reference evapotranspiration (ET₀), lifting irrigation demand; and (3) a more favourable late-season fire backdrop when compounded by wind events and low relative humidity.

Impacts across Chile — Precipitation

The rainfall signal is sharper and unmistakably El Niño-like. In May negative anomalies prevail over central-northern Chile (drier-than-average conditions), yet from June the imprint flips strongly: positive anomalies spread across south-central Chile with the clearest maximum in September.

Read May–October as a seasonal statement —not a deterministic date forecast— coherent with subtropical ridge shifts characteristic of constructing El Niño winters and springs over the South-east Pacific. Practically, the scenario suggests a partial claw-back of cumulative water deficits across central Chile, albeit uneven and concentrated in mid-to-late winter.

Takeaways

1. Building El Niño 2026. SEAS5 points to a moderate-to-strong event — anomalies pinned above +1 °C from June and peaking near +2.2 °C in October.
2. Warmer cordillera and north. Persistent positive temperature anomalies with expected repercussions for snow ablation, ET₀ and irrigation needs through spring.
3. Above-average rains in south-central Chile from August. After a dry-ish start September carries the rainfall maximum. Recovery of deficits is partial and patchy.
4. Amplified extremes. Storm clustering drives flood/conduit risk during winter while late-season fire weather risk can still elevate under the warm cordillera tail.