Two Ocean-Height Satellites Track El Niño's Heat as Hurricane Forecasts Retool

NASA's Jet Propulsion Laboratory says a pair of US-European radar altimetry satellites are measuring sea surface height across the Pacific during what its oceanographers expect to be a historic El Niño, and that the resulting data is being funnelled toward improved hurricane intensity forecasts.

In an article published on 9 September 2026, NASA said Sentinel-6B — launched last November with European partners — is now flying 30 seconds behind its predecessor, Sentinel-6 Michael Freilich. Together the two spacecraft make up the Copernicus Sentinel-6/Jason-CS (Continuity of Service) mission, which NASA describes as the latest in a series of ocean-observing altimetry missions that have monitored the seas continuously since the early 1990s.

A late-starting event, seen from orbit

"This El Niño was a late-bloomer," said Josh Willis, Sentinel-6B project scientist at NASA's Jet Propulsion Laboratory in Southern California. "It didn't kick off until the middle of the year and is just now reaching a strength similar to what we've seen in the satellite record during significant El Niños in 1997 and 2015. We expect it to be big, and it's already having big impacts."

NASA explains the physical chain behind those satellite measurements: the warmest ocean water normally sits along the equator in the western Pacific, but during El Niño the westward-blowing equatorial winds weaken and heat spreads eastward toward South America. That redistribution of ocean heat alters sea level, because warm water expands, and NASA says the shift moves hurricane activity from the Atlantic toward the Pacific.

Each Sentinel-6 satellite carries a radar altimeter that bounces thousands of radar pulses a second off wave crests and troughs, yielding ocean height along with wave size and marine wind speed. A second instrument, the Global Navigation Satellite System – Radio Occultation (GNSS-RO) package, measures atmospheric humidity, pressure and temperature.

Feeding the intensity forecast

NASA said Sentinel-6B began delivering low-latency data to scientists on 15 July, data that can be used for weather prediction. The agency cautioned that it will take time for the measurements to work their way into the research models meteorologists and climate scientists depend on.

According to NASA, data from the Sentinel-6 missions feeds hurricane tracking algorithms used by federal and state agencies, and those forecasts can trigger disaster response ranging from sandbag placement and National Guard activation to evacuation orders and, in more severe cases, engagement of the Federal Emergency Management Agency. NASA notes that while a tropical storm may take a week or more to become a hurricane and reach a coast, a hurricane can intensify rapidly in the final 48 hours before landfall.

"Hurricanes have been known to speed up quickly at the last moment, so the window in which to decide what to do is short," said Deirdre Byrne, an oceanographer and altimetry expert with the National Oceanic and Atmospheric Administration. "The goal is to forecast how much and how rapidly intensification will happen so that officials can make the right calls."

Byrne oversees NOAA's Satellite Ocean Heat Content Suite, which NASA says has been operating since 2012. She said she is most anticipating the ocean height data and plans to begin folding it into the current algorithm by the end of the year, adding: "In terms of data quality, the Sentinel-6 missions are unparalleled."

A record entering its fourth decade

NASA said the two satellites are also extending a precise sea level dataset into its fourth decade, a record that traces back to the TOPEX/Poseidon mission launched in 1992 and runs through Sentinel-6 Michael Freilich. Sentinel-6B is due to take over as the reference satellite for global sea level measurements later this year.

"The key is consistency, measuring the same way, every time," said Severine Fournier, Sentinel-6B deputy project scientist at JPL. "That's what lets us predict hurricanes, and, in turn, protect coastal communities and infrastructure."

Sentinel-6/Jason-CS sits within the European Union's Copernicus Earth observation programme and was jointly developed by ESA, EUMETSAT, NASA and NOAA, with funding support from the European Commission and technical support from the French space agency CNES. NASA said EUMETSAT handles spacecraft monitoring and control and processes all altimeter science data on behalf of Copernicus, while JPL contributed three instruments per satellite — the Advanced Microwave Radiometer, the GNSS-RO and the Laser Retroreflector Array — along with launch services and ground systems.

For background on how ocean observing systems underpin ENSO monitoring, see our science section.