Summary

NASA says Sentinel-6B and Sentinel-6 Michael Freilich are measuring ocean height, waves, marine winds and atmospheric properties during El Niño. The observations are intended to support hurricane-intensity forecasting, but no quantified improvement in forecast accuracy has yet been reported.

A pair of European and US satellites is collecting ocean and atmospheric measurements during an El Niño to help researchers understand conditions that influence hurricanes. NASA says the data from Sentinel-6B and Sentinel-6 Michael Freilich are intended to support more accurate storm-intensity forecasts, but the new satellite's observations have not yet been shown to improve forecast performance by a measured amount.

Contents

What changed

Sentinel-6B was launched in November 2025 by NASA and European partners. It is now flying approximately 30 seconds behind Sentinel-6 Michael Freilich, its predecessor, as part of the Copernicus Sentinel-6/Jason-CS Continuity of Service mission.

The two satellites form part of a continuous series of ocean-observing radar-altimetry missions that has monitored changing seas since the launch of TOPEX/Poseidon in 1992. Sentinel-6B began delivering low-latency data for possible use in weather prediction on July 15.

“Low latency” means the observations are made available relatively quickly for applications such as weather analysis, rather than being used only for long-term climate records. NASA says the data had not yet been incorporated into the research models used by meteorologists and climate scientists at the time described in its September 9 article.

Sentinel-6B is also expected to take over from Sentinel-6 Michael Freilich as the reference satellite for global sea-level measurements later in 2026. Maintaining a reference satellite helps preserve consistency across a long-running measurement series, while the paired observations extend continuity between successive missions.

How the satellites measure storm-relevant conditions

The satellites use radar altimeters to measure the height of the ocean surface, as well as wave size and marine wind speed. A radar altimeter sends thousands of radar pulses per second towards the ocean. The returning signals reflect from wave crests and troughs, and the timing of those returns is used to estimate sea-surface height.

Sea-surface height is relevant to hurricane forecasting partly because warm seawater expands. As a result, variations in ocean height can provide information about the distribution of heat in the upper ocean. Ocean height is not a direct thermometer, however: it is influenced by more than temperature and must be interpreted with other ocean and atmospheric observations.

Warm ocean water can provide energy to a tropical cyclone. Information about the amount and distribution of heat in the upper ocean can therefore help forecasting systems assess whether a storm may strengthen, including whether it may undergo rapid intensification. NASA says data from Sentinel-6 missions already feed hurricane-tracking algorithms used by federal and state agencies.

The Sentinel-6 satellites also carry Global Navigation Satellite System–Radio Occultation, or GNSS-RO, instruments. These instruments derive atmospheric information from how signals from navigation satellites are refracted as they pass through the atmosphere. The mission measures atmospheric humidity, pressure and temperature in addition to ocean conditions.

Combining these measurements is important because hurricane intensity depends on interactions between the ocean and atmosphere. The satellites are not standalone hurricane-forecasting systems. Their observations are inputs to algorithms and forecast models that also require other measurements and analysis.

Why El Niño makes the observations useful

El Niño changes the distribution of heat across the tropical Pacific. NASA describes the climate pattern as involving weakened equatorial winds and the eastward movement of Pacific Ocean heat. These changes can alter sea level and shift rainfall, storm and hurricane activity between the Pacific and Atlantic.

That makes the current conditions a useful setting for studying ocean-atmosphere interactions. NASA says the El Niño discussed in its article was reaching a strength comparable to events observed in the satellite record during 1997 and 2015.

The mission is intended to serve two purposes at once. Its long-running sea-level measurements support climate and ocean research, while the faster delivery of observations may provide information for near-term weather prediction. More timely information about ocean heat distribution could help forecasters evaluate how quickly hurricanes may intensify.

NOAA oceanographer Deirdre Byrne told NASA that she planned to begin incorporating Sentinel-6 ocean-height data into NOAA's Satellite Ocean Heat Content Suite algorithm by the end of 2026. NASA says that algorithm has operated since 2012. Whether the new observations produce a measurable improvement in hurricane-intensity forecasts remains to be evaluated.

Sources