Science & Technology (Commonwealth Union) – Since the El Niño was discovered in 1892 in Peru it has been a key focus for scientists tracking atmospheric phenomena.
Months before an El Niño develops, waves of warmer, elevated water travel eastward across the Pacific Ocean. Several of these waves have been detected in 2026 satellite observations.
Measurements of sea level from a satellite operated by NASA in collaboration with European partners reveal that a broad swell of warm water, stretching hundreds of miles, has reached the Pacific near the coast of South America. This pattern is a strong indicator that an El Niño event may occur later this year. As water warms, it expands, so rising ocean levels in a region signal increasing temperatures below the surface.
El Niño events can bring heavy rainfall to some areas and drought to others, affecting daily life, agriculture, and trade worldwide.
The Sentinel-6 Michael Freilich satellite, launched in 2020 by NASA and led by the European Space Agency for the EU’s Copernicus Programme, maps sea surface height across the global oceans every ten days with sub-inch precision. During El Niño, the satellite monitors eastward-moving warm waves known as Kelvin waves.
These waves generally develop after short periods when winds in the far western equatorial Pacific Ocean shift from their usual easterly direction — blowing from east to west — to westerlies. This shift, along with an overall weakening of the easterly winds along the equator, warms the tropical waters of the western Pacific and causes sea levels to rise. The resulting wave then travels eastward over several weeks, eventually reaching the coast of South America, where it further increases water temperatures and sea levels. An El Niño forms when multiple Kelvin waves appear over several months, leading to a buildup of warm water off the coasts of Colombia, Ecuador, and Peru.
Josh Willis, a sea level scientist at NASA’s Jet Propulsion Laboratory in Southern California and project scientist for Sentinel-6 Michael Freilich indicated that although this year’s event started slightly later than the major El Niños of 2015 and 1997, it is beginning to gain momentum.
He further indicated that that they have to wait and see how strong it becomes.
Data from Sentinel-6 Michael Freilich indicate that a small Kelvin wave formed near Micronesia in late January and faded by mid-February. Another wave emerged in early March and gradually moved eastward. By mid-May, sea levels around Peru were more than 5.9 inches (15 centimeters) above the long-term average.
“NASA’s observation of El Niño uses sea level satellites like Sentinel-6 Michael Freilich to track massive Kelvin waves as they cross the Pacific, capture changes in Earth’s ocean thermodynamics, improve forecasts of weather extremes, and help communities prepare for potential coastal hazards,” explained Nadya Vinogradova Shiffer, who is the lead program scientist at NASA Headquarters in Washington. “Stay tuned as more ocean stories continue to unfold.”
Warmer-than-usual sea surface temperatures in the central and eastern Pacific can influence global weather patterns by altering atmospheric circulation, including shifts in the jet stream. These changes redirect storm systems, which may bring intense rainfall and snowfall to some regions while triggering heatwaves and dry conditions in others. The extent of these effects largely depends on the intensity of the El Niño event.
During weaker episodes, such as those that began in 2018 and 2023, the most noticeable impacts—like droughts and flooding—tended to remain concentrated around the tropical Pacific region. In contrast, stronger events, such as the 2015–2016 El Niño, can have far-reaching consequences, contributing to drought conditions in parts of Africa and heavy flooding in regions like California.
El Niño events typically reach their peak between November and January, meaning the most significant global effects often become clearer several months after they first develop.
The JPL sea level researcher Séverine Fournier, deputy project scientist for Sentinel-6, Michael Freilich indicated every El Niño is unique, however they almost always make for a hot year and significant shifts in rainfall patterns across parts of the globe.
