El Niño is a climate pattern that develops when surface waters in the central and eastern tropical Pacific Ocean become unusually warm, weakening the trade winds that normally blow from the Americas toward Asia. This shift in ocean heat and wind direction triggers a chain reaction that alters weather across much of the globe, bringing floods to some regions, drought to others, and reshaping hurricane seasons, crop harvests, and disease patterns. It’s one half of a larger cycle called the El Niño-Southern Oscillation (ENSO), and it typically recurs every two to seven years.
How El Niño Forms
Under normal conditions, strong easterly trade winds push warm surface water westward across the Pacific, piling it up near Southeast Asia and Australia. Sea level near Indonesia actually sits higher than it does off the coast of South America. Cold, nutrient-rich water wells up along the western coast of the Americas to replace what’s been pushed away.
When El Niño begins, those trade winds weaken and sometimes reverse direction entirely. Without the winds holding warm water in the western Pacific, gravity pulls that massive pool of heated water back eastward toward the Americas. The ocean surface in the central and eastern Pacific heats up, and the atmosphere above it responds: high-pressure systems in the eastern Pacific weaken, air pressure shifts across the entire basin, and the jet stream changes course. NOAA officially classifies an event as El Niño when sea surface temperatures in a key monitoring region (called Niño 3.4) stay at least 0.5°C above average for five consecutive three-month periods.
Weather Shifts Across North America
As El Niño heats the central and eastern Pacific, it strengthens the jet stream and pushes it southward. That repositioned jet stream acts like a highway for storms, steering them into different parts of the continent than usual.
The southern United States typically sees cooler temperatures and more rain and storms during an El Niño winter. The northern U.S., by contrast, tends to be warmer and drier than normal. In the Pacific Northwest, states like Idaho, Oregon, and Washington generally experience milder, drier winters. Alaska follows a slightly different pattern: falls tend to be warmer and stormier, especially around the Gulf of Alaska, while winters turn warmer but drier.
Drought, Floods, and Fire in the Tropics
The effects flip dramatically on the other side of the Pacific. Southeast Asia and Australia, which normally receive abundant tropical rainfall, instead sit under a persistent high-pressure system that blocks moisture. The result is prolonged drought. During particularly strong El Niño years, this drying is severe enough to fuel massive wildfires. The 1997-98 event, one of the strongest on record, triggered fires across Indonesia that burned for months, made worse by the extreme drought even though many were initially set by humans.
Meanwhile, the normally arid Pacific coast of South America receives heavy, sometimes destructive rainfall and flooding. Peru and Ecuador are especially vulnerable. This reversal of wet and dry zones is one of El Niño’s most consequential features, because it affects regions that depend heavily on predictable seasonal rains for agriculture and water supply.
Effects on Hurricane Seasons
El Niño reshapes tropical storm activity in opposite directions depending on the ocean basin. In the Atlantic, it suppresses hurricanes. The mechanism comes down to vertical wind shear, the difference in wind speed and direction between lower and upper levels of the atmosphere. El Niño strengthens upper-level westerly winds over the Atlantic while reinforcing lower-level easterly trade winds. That mismatch tears apart developing storms before they can organize into hurricanes.
In the central and eastern Pacific, the opposite happens. Upper-level winds weaken, wind shear drops, and conditions become more favorable for tropical cyclones. So an El Niño year often means a quieter Atlantic hurricane season but a more active Pacific one.
Impacts on Food Production
El Niño’s reach extends into global agriculture. A study analyzing harvest data across major growing regions found that El Niño reduces average global yields of wheat by 1.32%, rice by 1.33%, and corn by 0.37%. Soybeans are an exception, with yields actually increasing by about 1.9% during El Niño years, likely due to favorable rainfall patterns in key soybean-growing areas like parts of South America.
The picture varies widely by region. Roughly 13% of the world’s rice-growing areas and nearly 12% of corn-growing areas show significant yield losses tied to El Niño conditions. For communities and countries that depend on a single staple crop, even modest percentage drops can translate into food insecurity, higher prices, and economic strain.
Disease Outbreaks Linked to El Niño
The combination of flooding in some regions and drought in others creates conditions for disease to spread. Malaria transmission has increased during past El Niño events globally, as warmer, wetter conditions expand the range of mosquitoes that carry the parasite. Waterborne diseases like cholera and leptospirosis intensify in countries hit by heavy rains and flooding, particularly in South America. Bolivia, Ecuador, Paraguay, and Peru have all recorded significant outbreaks of waterborne illness during strong El Niño years, with children especially vulnerable.
El Niño vs. La Niña
El Niño and La Niña are opposite phases of the same cycle. Where El Niño brings warmer-than-average Pacific waters and weakened trade winds, La Niña brings cooler-than-average waters and stronger trade winds that push even more warm water westward. La Niña shifts the jet stream northward over the eastern Pacific and weakens it, producing a roughly mirror-image set of weather effects: wetter conditions in the northern U.S. and Pacific Northwest, drier conditions in the southern U.S., and increased Atlantic hurricane activity.
Between these two phases, the Pacific often sits in a neutral state where neither pattern dominates. As of early 2026, La Niña conditions were active but weakening. NOAA’s Climate Prediction Center expected a transition to neutral conditions by spring 2026, with a 50 to 60% chance of El Niño forming by late summer 2026, though forecasts made this far in advance carry considerable uncertainty.