El Niño and La Niña are the two opposite phases of the same climate pattern in the tropical Pacific: El Niño is the unusual warming of the central and eastern Pacific Ocean, and La Niña is its cooling. Together they form the El Niño-Southern Oscillation (ENSO) cycle, which returns every few years and shifts rainfall and temperature over much of the planet, from California and the US South to Australia, Peru and southern Africa.
Key takeaways
- El Niño is a warming of the central and eastern tropical Pacific; La Niña is a cooling; the in-between phase is called neutral.
- NOAA declares El Niño when the sea temperature anomaly in the Niño 3.4 region is +0.5 °C (+0.9 °F) or more, and La Niña at −0.5 °C or less, sustained over several months.
- Each episode usually lasts 9 to 12 months and returns irregularly every 2 to 7 years.
- On October 8, 2026, NOAA kept an El Niño Advisory in place, with a Niño 3.4 anomaly of +2.1 °C and a strong to very strong event likely through January to March 2027.
- El Niño tends to bring a wetter southern US in winter and fewer Atlantic hurricanes; La Niña tends to do the opposite.
What is El Niño?
El Niño is a warming of several degrees in the surface water of the equatorial Pacific, from the middle of the ocean to the coasts of Peru and Ecuador. In normal years, the trade winds blow from east to west and pile warm water up near Indonesia and Australia, while cold, deep water rises off South America.
During El Niño the trade winds weaken, the warm water spreads east, and the belt of big tropical thunderstorms moves with it. That shift changes the jet streams and the path of storms across half the globe.
The name comes from Peruvian fishermen, who used it for the warm current that appeared some years around Christmas, after the Christ Child (el Niño in Spanish). The atmospheric half, the Southern Oscillation, is a seesaw of air pressure between Tahiti in the eastern Pacific and Darwin in northern Australia.
What is La Niña, and how is it different from El Niño?
La Niña is the cold phase of the same cycle: the trade winds blow harder than normal, the cold water off South America strengthens and the central Pacific cools. Its effects are, broadly, the opposite of El Niño's.
| El Niño | Neutral | La Niña | |
|---|---|---|---|
| Central and eastern Pacific water | Warmer | Normal | Cooler |
| Trade winds | Weak | Normal | Strong |
| Niño 3.4 anomaly (NOAA) | +0.5 °C or more | −0.5 to +0.5 °C | −0.5 °C or less |
| US southern tier in winter | Wetter, cooler | No clear signal | Drier, warmer |
| Atlantic hurricanes | Fewer | Normal | More |
| Eastern Australia | Drier, hotter days | Normal | Wetter, flood risk |
| Coast of Peru and Ecuador | Heavy rain | Normal | Drier and cooler |
| Global average temperature | Up a tenth or two | No effect | Slightly down |
La Niña can last longer than El Niño and repeat for several winters in a row, as it did from 2020 to 2023.
How does NOAA define El Niño and La Niña?
NOAA's Climate Prediction Center (CPC) declares El Niño when the sea surface temperature in the Niño 3.4 region is 0.5 °C (0.9 °F) or more above normal, and La Niña when it is 0.5 °C or more below. Niño 3.4 is a strip of the central equatorial Pacific between 5° N and 5° S and between 170° W and 120° W.
One warm month is not enough. The CPC uses three-month averages, and the anomaly must last five overlapping three-month periods for the episode to enter the historical record. In 2026 NOAA adopted the relative index RONI as its main measure: it compares Niño 3.4 with the average of the whole tropics, correcting for the general warming of the oceans that made recent values look warmer.
Episodes are commonly graded as weak (0.5 to 0.9 °C), moderate (1.0 to 1.4 °C), strong (1.5 to 1.9 °C) and very strong (2.0 °C or more). Australia's Bureau of Meteorology uses a higher threshold, +0.8 °C on its relative Niño 3.4 index, so the two agencies do not always declare an event at the same time.
Is it El Niño or La Niña in 2026?
It is El Niño: the latest CPC diagnostic discussion, published on October 8, 2026, kept the El Niño Advisory in place and described the event as strengthening. The Niño 3.4 anomaly reached +2.1 °C in September, and NOAA gave a greater than 83% chance of a strong to very strong El Niño through January to March 2027.
So there is no La Niña in 2026 anymore. The La Niña of the 2025-26 winter ended in March 2026, when NOAA issued its final La Niña Advisory, and the Pacific then warmed quickly through the spring and summer. After a big El Niño, the cycle often swings toward neutral or La Niña the following year, but whether a La Niña develops in 2027 cannot be forecast reliably yet.
The CPC updates its discussion once a month, usually on the second Thursday; the next is due on November 12, 2026. If you read this later, check the latest NOAA or Bureau of Meteorology update.
How do El Niño and La Niña affect US weather?
El Niño and La Niña mostly affect US weather from October to March, when they push the Pacific jet stream south or north. They shift the odds for a season; they do not decide what happens on a given day.
El Niño vs La Niña weather in California
During El Niño the Pacific jet stream tends to run farther south and east, so Southern California and the southern tier get more storms and a wetter winter than usual. NOAA's winter outlook for December 2026 to February 2027 favors wetter than normal conditions from the Southwest to the Southeast and along the East Coast, and a warmer than normal winter for northern California, the Pacific Northwest and much of the North.
La Niña usually pushes the storm track north: the Pacific Northwest tends to be wetter and colder, while Southern California, Texas and the Southeast tend to be drier and warmer. Even a very strong El Niño does not guarantee a wet winter everywhere in California.
El Niño vs La Niña and the hurricane season
El Niño usually means fewer Atlantic hurricanes, because it increases the wind shear over the Caribbean that tears developing storms apart. It favors more hurricanes in the eastern and central Pacific. La Niña does the opposite and tends to boost the Atlantic season. We explain the role of wind shear in how do hurricanes form.
How do El Niño and La Niña affect Australia and the rest of the world?
In Australia, El Niño usually brings below average rain and hotter days to much of the eastern half of the country, raising drought and bushfire risk, while La Niña brings wetter conditions and floods. In Southeast Asia, including Indonesia and the Philippines, El Niño tends to bring drought.
In South America, El Niño brings heavy rain and floods to normally dry coastal Peru and Ecuador, and warmer water drives the anchovy away. In Colombia it reduces rainfall and raises the risk of fires and low reservoirs; in 2024 Bogotá rationed water after an El Niño dry spell. In Argentina it tends to bring more spring and summer rain to the Pampas, while La Niña is linked to drought, as in 2022-2023. You can follow the weather in Lima or the 14 day forecast for Buenos Aires.
In the UK and Spain the effect is weak, because their weather depends mainly on the North Atlantic. Some studies find small links with winter or autumn rain, but the signal is too weak to forecast a particular season.
Where El Niño does show up is in global temperature: years with a strong El Niño often set world records, because the Pacific releases heat into the atmosphere. You can see it in the hottest and coldest temperatures on record.
How to use Clima de Hoy in an El Niño year
El Niño changes the odds over a season, but each day's weather still depends on specific storms and fronts. To plan, combine the seasonal outlook from your national weather service with the local forecast: Clima de Hoy has hourly, 7 and 14 day forecasts for each city, such as Mexico City. If you live in an area with a strong El Niño signal, such as Southern California, northern Peru or eastern Australia, check the rain forecast more often during the months of greatest impact.
Frequently asked questions
What is El Niño in simple terms?
El Niño is an unusual warming of the tropical Pacific Ocean, off Peru and Ecuador and in the middle of the ocean. The extra heat changes winds and rainfall over much of the world for several months. It returns irregularly every 2 to 7 years.
What is the difference between El Niño and La Niña?
El Niño is the warm phase of the ENSO cycle and La Niña is the cold phase. With El Niño the central and eastern Pacific warms and the trade winds weaken; with La Niña it cools and the trade winds strengthen. Their effects on rainfall are usually opposite.
Is El Niño or La Niña better for California?
El Niño usually raises the odds of a wet winter in Southern California, which helps with drought but brings flood and mudslide risk. La Niña tends to bring a drier winter to Southern California and a wetter one to the Pacific Northwest. Neither phase guarantees the outcome in a given year.
How long does El Niño last?
An El Niño episode usually lasts 9 to 12 months and normally peaks late in the year, between November and January. La Niña sometimes lasts longer and can repeat for several years. NOAA only ends an episode when the anomaly returns to the neutral range.
Does El Niño cause climate change?
No. El Niño is a natural variation that has existed for thousands of years, while current climate change is driven mainly by greenhouse gases from human activity. But the two add up: a strong El Niño on a warmer planet makes new global temperature records more likely.
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