El Niño and La Niña are complex weather phenomena resulting from ocean temperature fluctuations in the Equatorial Pacific.
Higher-than-normal sea-surface temperatures in the Pacific Ocean characterize El Niño. During this phase, the trade winds weaken, causing warm water to move eastward toward the West Coast. In contrast, La Niña involves cooling sea-surface temperatures in the east-central equatorial Pacific. La Niña events are marked by stronger-than-normal trade winds that drive warm water toward Asia. These variations lead to significant global weather impacts.
El Niño and La Niña episodes generally last from nine to 12 months, though they can occasionally persist for several years. These events typically occur every two to seven years, but they don’t occur on a regular schedule. Generally, El Niño tends to happen more often than La Niña. As opposing phases of the El Niño-Southern Oscillation (ENSO), they cannot occur at the same time, and there are many periods when neither is present.
What is ENSO?
The El Niño-Southern Oscillation (ENSO) is a term used to describe the variations in the equatorial Pacific’s ocean surface temperatures and air pressure.
When sea-surface temperatures rise above average by about 1 degree Fahrenheit or more, El Niño can develop. Conversely, when temperatures dip below average, La Niña may develop. In ENSO-neutral conditions, temperatures hover around average, preventing the formation of either phenomenon.
The air pressure component involves comparing pressure differences between the western and eastern equatorial Pacific. Readings are taken from Darwin, on Australia’s north-central coast, and Tahiti, over 5,000 miles to the east. Lower-than-normal pressure in Tahiti and higher-than-normal pressure in Darwin favor El Niño development, while the reverse supports La Niña.
Both temperature and air pressure conditions must align for either El Niño or La Niña to occur.
How do El Niño and La Niña impact the weather?
El Niño and La Niña have minimal impact on summer climate in the United States; the most substantial influence occurs in winter.
During El Niño events, the jet stream typically moves southward, leading to rainier and cooler weather across much of the Southern US while bringing warmer conditions to the Northern US. Globally, El Niño can result in warm, dry weather in regions such as Asia, Australia, and India, and influence weather patterns in parts of Africa and South America. El Niño impacts marine life by disrupting the upwelling of cold, nutrient-rich water along the Pacific coast, leading to a decline in phytoplankton and affecting the entire marine food chain.
With La Niña, the jet stream shifts northward, leading to warm and dry conditions in the Southern US and cooler, wetter weather in parts of the Northern US, especially the Pacific Northwest. La Niña can also lead to a more severe hurricane season. Globally, parts of Australia and Asia can be wetter than usual. During La Niña, the Pacific coast experiences colder, nutrient-rich waters, which support increased marine life and draw more cold-water species to regions like the California coast.
How does El Nino & La Nina affect California?
During El Niño, California often experiences wetter and cooler conditions, which can lead to increased rainfall and potential flooding. These heavy rains can contribute to mudslides and affect agriculture by both replenishing water supplies and causing crop damage.
Conversely, La Niña tends to bring drier and warmer conditions, exacerbating droughts and increasing the risk of wildfires. The lack of precipitation during La Niña can strain water resources, impacting both agricultural production and urban water supply.
In Northern California, there is little correlation between precipitation and most ENSO patterns, according to the National Weather Service. They note that Southern California is generally much more impacted with El Nino conditions bringing higher than normal precipitation and La Nina bringing below normal precipitation to Southern California.
So there are no guarantees. Not every El Niño period is extra wet in the Golden State, and not every La Nina means a dry year. However, between 50 and 70 percent of El Niños since 1950 have led to above-average winter precipitation in California, according to the National Weather Service, which gives a slight edge to wet El Nino years.
Coverage of El Niño and La Niña on Maven ‘s Notebook
COURTHOUSE NEWS: El Niño events much stronger in past several decades
Scientists documented changes in sea temperature by coral growth over time to evaluate the intensity of bygone and more recent El Niño events. By Carly Nairn, Courthouse News Service El Niños have come and gone for ages, but recent findings suggest extreme weather events caused by their effects are 40% stronger in the last few decades than in the 19th century. In a study published Thursday in the journal Science, researchers at the University of Michigan examined ancient and modern […]
NASA: El Niño alters marine life in the Pacific
From JPL: As of June 2026, El Niño has officially arrived. This naturally recurring phenomenon is characterized by warmer-than-normal water temperatures in parts of the equatorial Pacific along with changes to atmospheric and oceanic circulation patterns. Its regional effects range from desert floods to delayed monsoons to shifts in where tropical cyclones are more likely to form. NOAA’s Climate Prediction Center expects the current El Niño to continue to strengthen through the end of 2026, with a 97 percent chance of […]
CAL MATTERS: Fierce floods or wild waves? How San Diego is preparing for a winter of extreme weather under El Niño.
As a “super El Niño” season gains steam, San Diego contends with aging stormwater systems and century-old dams. By Deborah Brennan, CalMatters This story was originally published by CalMatters. Sign up for their newsletters. When the super El Niño arrives this winter, San Diego could be in for raging floods that gush through canyons and hillsides. Or it could face sparse rainfall and heightened fire risk. It could also see monster waves carve away beaches and pummel piers. El Niño, […]
INSIDE CLIMATE NEWS: This year’s El Niño could spell disaster for West Coast fishermen
Warming waters will severely disrupt food chains, leaving West Coast crews unable to catch commercial stocks, warn ocean advocates. By Johnny Sturgeon This article originally appeared on Inside Climate News, a nonprofit, non-partisan news organization that covers climate, energy and the environment. Sign up for their newsletter here. The last El Niño was linked to severe droughts in Southern Africa, wildfires in Indonesia and global coral bleaching. Now, ocean advocates are warning that American fishermen could face significant financial losses […]
SJV WATER: Will the “super” El Niño fill Tulare Lake? A Fresno engineer thinks it’s almost certain
By Lois Henry, SJV Water El Niño is coming. Of that, scientists seem sure as ocean temperatures continue to heat up. Warmer ocean water fills the atmosphere with moisture, which can ride the jet stream into California as massive storms. Or not. Weather is such a tricky beast. Regardless of whether this pattern becomes a “monster,” “Godzilla,” “Jurassic,” or just plain vanilla “super” El Niño, Fresno Engineer John Ennis has found an historic quirk that he believes can result in […]
Read all coverage on Maven’s Notebook.