NASA and its European partners are tracking a large buildup of warm water in the Pacific Ocean that could be a sign of El Niño arriving later this year.
Data collected by the Sentinel 6 Michael Freilich satellite shows that large swathes of unusually warm water are reaching waters hundreds of miles off the coast of South America. Water expands when it warms, so rising sea levels in certain areas of the ocean can reveal areas where temperatures are rising beneath the surface.
El Niño can have widespread effects, bringing excessive rain to some areas and making others abnormally dry. These changes could impact agriculture, transportation, water resources, and economies around the world.
Satellite data reveals warm waters in the Pacific Ocean
Sentinel 6 Michael Freilich, launched by NASA in 2020 and led by ESA (European Space Agency) for the EU Copernicus mission, measures the sea level of the world’s oceans to a fraction of an inch every 10 days. One of its key roles is to monitor warm ocean features known as Kelvin waves, which are closely associated with the occurrence of El Niño.
Kelvin waves typically begin when wind patterns in the far western equatorial Pacific temporarily change direction. Instead of the usual easterly winds that blow from east to west, westerly winds develop. Combined with widespread weakening of easterly winds along the equator, this allows for increased temperatures and sea levels in the tropical waters of the western Pacific Ocean.
The resulting wave of warm water travels eastward across the Pacific Ocean over several weeks. Once it reaches South America, ocean temperatures and sea levels near the coast will rise. El Niño is formed when these Kelvin waves occur over several months and warm water accumulates along the coasts of Colombia, Ecuador, and Peru.
“This year’s event started a little later than the big El Niños of 2015 and 1997, but it’s starting to catch up,” said Josh Willis, a sea surface researcher at NASA’s Jet Propulsion Laboratory in Southern California and Sentinel 6 project scientist. “Let’s see how big it gets.”
Satellite observations showed that small Kelvin waves form near Micronesia in late January and dissipate by mid-February. Another wave formed in early March and moved steadily eastward. By mid-May, sea levels near Peru were more than 15 centimeters above the long-term average.
“NASA’s El Niño observations use ocean surface satellites like Sentinel 6 Michael Freilich to track giant Kelvin waves across the Pacific Ocean, capturing changes in Earth’s ocean thermodynamics, improving predictions of extreme weather events, and helping communities prepare for potential coastal hazards,” said Nadia Vinogradova Schiffer, chief program scientist at NASA Headquarters in Washington. “Please look forward to more sea stories that will unfold in the future.”
How El Niño affects global weather
The term El Niño dates back to the 1600s. At that time, fishermen noticed that the rise in ocean temperatures was often stronger around Christmas. They called the phenomenon El Niño, which means “boy” in Spanish, after the birth of baby Jesus. Rising sea temperatures have also reduced fish catches.
Rising sea surface temperatures in the central and eastern Pacific Ocean could change atmospheric circulation around the world. One important effect is changes in the jet stream, which affect the path of the storm. As a result, some regions are experiencing heavy rain or snowfall, while others are experiencing unusually hot and dry conditions.
The geographic extent of these impacts depends largely on the intensity of the event. Milder El Niño events, such as those that began in 2018 and 2023, caused droughts and floods primarily in and around the tropical Pacific region. More powerful events, such as the 2015-2016 El Niño event, had effects farther afield, contributing to droughts in Africa and floods in California.
El Niño events typically peak between November and January, so it will be several more months before the full extent of this year’s impact becomes clear.
“Every El Niño is different,” said Sébrine Fournier, a sea surface researcher at JPL and Sentinel 6’s deputy project scientist. “But they almost always result in extreme heat and large changes in precipitation in some parts of the globe.”
Sentinel-6 continues decades of ocean surface monitoring
Sentinel-6 Michael Freilich currently serves as the official reference satellite for measuring global sea levels. This mission continues a record that began with the 1992 TOPEX/Poseidon launch. Since then, a series of satellites have expanded its long-term dataset. The newest satellite in the series, Sentinel 6B, is scheduled to launch in November 2025 and take on this mission by the end of 2026.
Learn more about Sentinel-6 Michael Freilich
Sentinel 6 Michael Freilich, named for former NASA Earth Sciences Director Michael Freilich, is one of two satellites that make up the Copernicus Sentinel 6/Jason CS (Continuation of Service) mission.
Sentinel-6/Jason-CS is part of the European Union’s Copernicus Earth Observation Program. The mission was jointly developed by ESA, the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), NASA, and the National Oceanic and Atmospheric Administration (NOAA). Financial support was provided by the European Commission, and the French space agency CNES (Centre National d’Études Spatials) provided technical support related to mission execution.
EUMETSAT will operate and monitor the spacecraft on behalf of the European Union’s Copernicus program and will process all altimeter science data in collaboration with the mission’s partner institutions.
NASA’s Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, provided three science instruments for each Sentinel-6 satellite: an advanced microwave radiometer, a Global Navigation Satellite System – radio occultation, and a laser retroreflector array.
NASA also provided launch services, ground systems used to operate NASA instruments, scientific data processing systems for two of those instruments, and support for U.S. members of the International Ocean Surface Topography Science Team.
