How El Niño and La Niña drive seasonal predictability
ENSO is a major source of seasonal predictability. How Pacific sea-surface temperatures shape the coming season, where the effect is strong and where it is weak.
A major source of seasonal signal
The El Niño–Southern Oscillation, or ENSO, is a coupled swing of the tropical Pacific between warm (El Niño), cold (La Niña) and neutral states. Because it involves the upper ocean, it evolves over months and can often be predicted several months ahead. Skill depends on the event and season, with a particular challenge for forecasts crossing boreal spring. ENSO is a major source of seasonal predictability, but its influence is not equally strong everywhere.
How the ocean reaches the atmosphere
Tropical convection responds to sea-surface temperatures and their spatial contrasts, together with atmospheric conditions. When El Niño shifts warm water eastward, the main region of rising air moves with it, and the change in tropical heating launches wave trains through the atmosphere that alter the jet streams over both hemispheres. These remote responses are called teleconnections. Their strength and pattern depend on season and event. They can appear in seasonal models as anomalies in mean sea-level pressure, which is why this site includes a pressure field alongside temperature and precipitation.
Where the effect is strong
The tropical Pacific itself, the maritime continent, Australia, parts of southern Africa, eastern Africa, India and the Americas have well-documented ENSO responses. In North America, El Niño winters tend to be wetter across the southern United States and milder across the north. These are tendencies, not guarantees; models differ in how well they represent them. The SST maps here show the predicted Pacific pattern.
Where the effect is weak
ENSO’s European effects depend on the season and atmospheric circulation. Other influences, including the stratospheric polar vortex and North Atlantic sea-surface temperatures, also matter. ENSO alone is therefore insufficient to infer Europe’s seasonal outlook; see how seasonal forecast skill varies between the tropics and Europe.
Reading ENSO on the maps
Select the sea-surface temperature field and the global region. A warm or cool anomaly pattern in the central/eastern equatorial Pacific can suggest an El Niño-like or La Niña-like outlook. It is not enough to diagnose an event: ENSO involves persistent ocean anomalies and a coupled atmospheric response. These maps use model-relative 1993–2016 anomalies, not an official observed ENSO index. Compare forecasts for the same valid period to assess how the outlook has changed, and consult an operational ENSO assessment for event status.
Sources and method
These references explain the underlying science and provider conventions. Descriptions of this site’s calculations, colours and coverage were checked against its processing code and imported data.
- NOAA: ENSO and its ocean–atmosphere components
- NOAA: the ENSO spring predictability barrier
- C3S seasonal product definitions