Sentinel-6 satellite data shows strengthening warm-water waves in the Pacific, pointing to the likely arrival of El Niño and its global weather impacts later in 2026.
Several months before an El Niño develops, large waves of warmer, elevated water travel eastward across the Pacific Ocean. Satellite observations in 2026 have detected several of these waves.
Sea level measurements collected by a satellite operated by NASA and its European partners reveal that a broad mass of warm water, stretching hundreds of miles across, has reached the Pacific Ocean near South America. Scientists view this as a strong indication that El Niño could form later this year. Since water expands as it warms, higher ocean surface levels are a sign of increasing temperatures below.
El Niño events can bring unusually heavy rainfall to some parts of the world while causing dry conditions in others, affecting communities, agriculture, transportation, and economies worldwide.
Sentinel-6 Tracks El Niño’s Early Warning Signs
Launched in 2020 by NASA and managed by ESA (European Space Agency) for the E.U. Copernicus Program, the Sentinel-6 Michael Freilich satellite measures ocean surface height across the globe every 10 days with precision down to fractions of an inch. For El Niño monitoring, the mission focuses on warm Kelvin waves.
These waves often develop when winds over the western equatorial Pacific briefly reverse direction, changing from easterlies that normally blow from east to west to westerlies. Combined with a broader weakening of easterly winds along the equator, this shift allows waters in the western tropical Pacific to warm and sea levels to rise.
The international Sentinel-6 Michael Freilich sea level satellite observed a swell of warm water, called a Kelvin wave, moving eastward in the equatorial Pacific Ocean, arriving off the South American coast in May. Warm Kelvin waves often precede El Niño events. Credit: NASA/JPL-Caltech
The resulting wave then moves eastward for weeks, eventually reaching South America, where it raises ocean temperatures and sea levels along the coast. El Niño takes shape when several Kelvin waves occur over a period of months, allowing warm water to build up near Colombia, Ecuador, and Peru.
“While this year’s event started a bit later than the big El Niños of 2015 and 1997, it’s beginning to catch up,” said Josh Willis, a sea level researcher at NASA’s Jet Propulsion Laboratory in Southern California and project scientist for Sentinel-6 Michael Freilich. “We’ll see how big it gets.”
Kelvin Waves Raise Sea Levels Near South America
Data from Sentinel-6 Michael Freilich detected a small Kelvin wave forming near Micronesia in late January before fading by mid-February. Another wave appeared in early March and gradually traveled eastward. By mid-May, sea levels near Peru were more than 5.9 inches (15 centimeters) higher than 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,” said Nadya Vinogradova Shiffer, lead program scientist at NASA Headquarters in Washington. “Stay tuned as more ocean stories continue to unfold.”
The term El Niño was first used by fishermen in the 1600s. The Spanish phrase means “the boy,” referring to the birth of baby Jesus, because the warming event often intensified around Christmas. They also noticed that warmer waters reduced fish catches.
How El Niño Reshapes Global Weather Patterns
Higher sea surface temperatures in the central and eastern Pacific alter atmospheric circulation around the world by shifting the jet stream and changing storm tracks. As a result, some regions experience heavier rain and snow, while others face unusual heat and dry conditions. The extent of these impacts depends on the strength of the El Niño event.
During weaker events, such as those that began in 2018 and 2023, drought and flooding effects were largely confined to areas in and around the tropical Pacific. Stronger events, including the 2015-2016 El Niño, can have much broader consequences, contributing to drought in Africa and flooding in California.
El Niño events typically reach their peak between November and January, meaning the most significant effects of the current event may not become apparent for several more months.
“Every El Niño is different,” said JPL sea level researcher Severine Fournier, deputy project scientist for Sentinel-6 Michael Freilich. “But they almost always make for a hot year and big changes in rainfall in parts of the globe.”
Sentinel-6 Mission Continues Sea Level Monitoring Legacy
Sentinel-6 Michael Freilich now serves as the official reference satellite for tracking global sea levels. Launched in 2020, it extends a record that began with the TOPEX/Poseidon satellite in 1992. Several follow-up missions have continued that work, and Sentinel-6B, launched in November 2025, is expected to replace Sentinel-6 Michael Freilich by the end of 2026.
Sentinel-6 Michael Freilich, named after former NASA Earth Science Division Director Michael Freilich, is one of two satellites that compose the Copernicus Sentinel-6/Jason-CS (Continuity of Service) mission.
Sentinel-6/Jason-CS, a part of the European Union’s Earth observation program called Copernicus, was jointly developed by ESA, the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), NASA, and the National Oceanic and Atmospheric Administration (NOAA), with funding support from the European Commission and technical support on performance from the French space agency CNES (Centre National d’Études Spatiales). Spacecraft monitoring and control, as well as the processing of all the altimeter science data, is carried out by EUMETSAT on behalf of the European Union’s Copernicus Programme, with the support of all partner agencies.
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