El Niño vs La Niña: What They Are and How They Shape Your Winter Weather

El Niño and La Niña are the warm and cool phases of a natural climate pattern in the tropical Pacific Ocean that shifts weather around the world. Right now a powerful El Niño is under way: in its October 2026 update, the US National Oceanic and Atmospheric Administration (NOAA) said a strong to very strong El Niño is likely to last through January to March 2027, with sea temperatures in parts of the eastern Pacific more than 4°C above normal. This guide explains what El Niño and La Niña are, how scientists measure them, how they affect weather in the US and around the world, and what this winter’s event could mean for you.

What Is El Niño?

El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO), a cycle of changes in ocean temperatures and winds across the equatorial Pacific. Normally, trade winds blow from east to west, pushing warm surface water towards Asia and Australia and allowing cold water to rise along the coast of South America.

During El Niño, those trade winds weaken or even reverse. Warm water spreads east towards the Americas, the upwelling of cold water slows, and rainfall shifts from the western to the central and eastern Pacific. Because the ocean and atmosphere are linked, these changes alter the path of the jet stream and weather patterns thousands of miles away.

The name means “the little boy” in Spanish and was used by Peruvian fishermen who noticed warm water appearing around Christmas.

What Is La Niña?

La Niña, “the little girl”, is the cool phase. The trade winds strengthen, more warm water is pushed west and cooler-than-normal water covers the central and eastern Pacific. Its effects on weather are often roughly the opposite of El Niño’s. Between the two is a neutral phase, when conditions are close to average.

How Do Scientists Measure El Niño and La Niña?

NOAA’s Climate Prediction Center tracks sea surface temperatures in a key region of the Pacific called Niño-3.4. In simple terms:

• El Niño conditions: the region is at least 0.5°C warmer than average and the atmosphere responds
• La Niña conditions: at least 0.5°C cooler than average
• Strength: anomalies around 1.5°C or more are generally considered strong, and above 2°C very strong
• Relative index: NOAA now also uses a relative index that compares the region with the rest of the tropics, to separate El Niño from overall ocean warming caused by climate change

Events usually develop in the Northern Hemisphere spring or summer, peak in winter and fade the following spring. The cycle is irregular, with El Niño or La Niña typically occurring every two to seven years.

How Strong Is the Current El Niño?

NOAA’s ENSO Diagnostic Discussion issued on 8 October 2026 kept an El Niño Advisory in place and reported:

• Weekly sea temperatures in the Niño-3.4 region about 2.1°C above average, with the Niño-3 region about 3.0°C and the Niño 1+2 region near the South American coast about 3.9°C above average
• Anomalies exceeding +4°C in parts of the eastern Pacific
• A greater than 83% chance of a strong to very strong El Niño persisting through January to March 2027
• A significant chance of a historically strong event, comparable to 1982-83, 1997-98 and 2015-16

NOAA updates its outlook monthly, with the next discussion due on 12 November 2026, so expect the forecast to be refined as winter approaches.

How Does El Niño Affect US Weather?

El Niño’s influence on the US is strongest in winter. Typical patterns, although never guaranteed, include:

• Wetter and stormier southern US: California, the Gulf Coast and Florida often see more rain and flooding risk
• Milder northern US and Canada: the northern Plains, Great Lakes and western Canada tend to be warmer and drier than usual, with less snow
• Drier Ohio Valley and Pacific Northwest in many El Niño winters
• Fewer Atlantic hurricanes: stronger wind shear over the Atlantic tends to suppress hurricane activity, while the eastern and central Pacific often see more storms

La Niña winters tend to bring the reverse: a drier, warmer southern US, which increases drought and wildfire risk in the Southwest, and a colder, snowier north. La Niña also tends to favour a more active Atlantic hurricane season. Our explainer on hurricanes vs tornadoes covers how those storms form.

How Does El Niño Affect the Rest of the World?

• Peru and Ecuador: heavy rain, flooding and landslides along the coast, and a collapse in anchovy fishing as warm water drives fish away
• Australia, Indonesia and the Philippines: higher risk of drought, heatwaves and bushfires
• India: weaker monsoon rains in many El Niño years, affecting farming
• Southern Africa and Central America: often drier, with risks to crops
• Global temperatures: El Niño releases heat from the ocean into the atmosphere, so years during or after strong events often set global heat records, as in 1998, 2016 and 2023-24

What Usually Happens After a Strong El Niño?

Strong El Niño events often fade during the following spring, and it is common for the Pacific to swing towards neutral conditions or La Niña within a year or so. That happened after the powerful 1997-98 and 2015-16 events, both of which were followed by La Niña. Such a switch is not guaranteed, however, and forecasts made in spring are notoriously less reliable, a problem scientists call the “spring predictability barrier”. For planning beyond the coming winter, it is best to rely on NOAA’s monthly updates rather than on what happened after past events.

Is Climate Change Making El Niño Worse?

Scientists are still studying how climate change affects ENSO itself, and models disagree about whether events will become more frequent or more intense. What is clearer is that El Niño now arrives on top of a warmer baseline. That means its heat, heavy rain and drought can be more extreme than in the past. Our guide to the greenhouse effect explains the underlying warming.

How Can You Prepare for an El Niño Winter?

• Follow official forecasts: check NOAA’s seasonal outlooks and your local National Weather Service office, or Environment Canada, rather than relying on long-range rumours
• Review flood risk: in California and the southern US, clear gutters and drains, and consider flood insurance, which usually has a 30-day waiting period under the National Flood Insurance Program
• Prepare for power cuts: keep torches, batteries and a basic emergency kit
• Plan travel flexibly: storms can disrupt flights and roads, so consider travel insurance for winter trips
• Farmers and businesses: factor seasonal outlooks into planting, stock and energy decisions
• Watch food prices: strong events can affect crops such as cocoa, coffee, rice and palm oil

The Bottom Line

El Niño and La Niña are two sides of the same Pacific climate cycle. El Niño warms the eastern Pacific and tends to bring a wetter southern US, a milder north and fewer Atlantic hurricanes; La Niña largely does the opposite. With NOAA forecasting a strong to very strong El Niño through early 2027, this winter could bring significant weather impacts, so keep an eye on official forecasts and prepare early.

Featured image: JMC 3208 (32149486630), by Ministerio de Defensa del Perú / Wikimedia Commons, CC BY 2.0. Cropped, colour-graded and combined with MediaPavilion branding.

Sources

• NOAA Climate Prediction Center — ENSO Diagnostic Discussion (8 October 2026).
• NOAA Climate.gov — What is the El Niño-Southern Oscillation (ENSO) in a nutshell? (accessed 2 November 2026).
• NOAA National Ocean Service — What are El Niño and La Niña? (accessed 2 November 2026).
• World Meteorological Organization — El Niño/La Niña Update (accessed 2 November 2026).
• FEMA — National Flood Insurance Program (accessed 2 November 2026).