Sea level data from a satellite launched by NASA and European partners shows that a swell of warm water hundreds of miles wide has arrived in the Pacific Ocean off the coast of South America, a sign that El Niño will likely emerge later in the year. Because water expands as it warms, a rise in elevation of an area of the ocean indicates increasing ocean temperatures.
El Niños can cause heavy precipitation in some regions and deficits in others, influencing daily life and commerce around the world.
Launched in 2020 by NASA and led by ESA (European Space Agency) for the E.U. Copernicus Programme, the Sentinel-6 Michael Freilich satellite measures and maps water height for the entire ocean every 10 days, down to fractions of an inch. In the case of El Niño, the satellite tracks what are called warm Kelvin waves.
These waves typically form after brief periods when winds over the far western equatorial Pacific Ocean shift from prevailing easterlies — moving from east to west — to westerlies. That effect, combined with a general weakening of easterly winds along the equator, causes water in the tropics of the western Pacific to get warmer and sea levels to rise. The wave that forms then propagates east for several weeks, eventually reaching South America and causing water off the coast to heat up and rise. An El Niño develops as multiple Kelvin waves appear over the course of several months, and the warm water accumulates off the shores of Colombia, Ecuador, and Peru.
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“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.”
Measurements from Sentinel-6 Michael Freilich show a small Kelvin wave forming around Micronesia in late January and dissipating by mid-February. A new wave emerged in early March, then moved east over time. By mid-May, the seas around Peru were more than 5.9 inches (15 centimeters) higher than long-term averages.
“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.”
Tracking El Niño
Fishermen in the 1600s coined the name El Niño — Spanish for “the boy,” a reference to the birth of baby Jesus — because it tended to intensify around Christmastime. Warmer waters meant they would catch fewer fish.
Warmer sea surface temperatures in the central and eastern Pacific affect atmospheric circulation patterns worldwide by shifting the jet stream, which impacts storm tracks. This can lead to heavy rain and snow in some areas and unusual heat and dryness in others. How far away those impacts appear depends on the strength of the El Niño.
In more modest events, like the ones that began in 2018 and 2023, impacts such as drought and flooding were mostly seeb in and around the tropical Pacific. Large El Niños, like the one in 2015-2016, reach much farther, causing drought in Africa and flooding in California.
El Niños usually peak between November and January, so it will be several months before the largest impacts become clear.
“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 Michael Freilich is the current official reference satellite for global sea level measurements. Launched in 2020, it is continuing a legacy started in 1992 by the TOPEX/Poseidon satellite. A series of successors have carried the baton since then, and the latest, Sentinel-6B, which launched November 2025, will take over for its predecessor by the end of 2026.
More about Sentinel-6 Michael Freilich
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 programme called Copernicus, was jointly developed by ESA, the European Organisation 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.
A division of Caltech in Pasadena, JPL contributed three science instruments for each Sentinel-6 satellite: the Advanced Microwave Radiometer, the Global Navigation Satellite System - Radio Occultation, and the Laser Retroreflector Array. NASA also contributed launch services, ground systems supporting operation of the NASA science instruments, the science data processors for two of these instruments, and support for the U.S. members of the international Ocean Surface Topography Science Team.
To learn more about Sentinel-6 Michael Freilich, visit: