Far from any coastline, in waters few ships ever cross, an invisible storm trail has been rolling across the Pacific.
What began as a fierce but distant low-pressure system has turned into one of the most striking wave events ever measured, with satellites now capturing walls of water as tall as a ten-storey building as they travel silently around the globe.
When the Pacific builds 35-metre walls of water
At the end of 2024, a powerful storm nicknamed Eddie ripped through the North Pacific. It barely made headlines on land. It never slammed directly into major coastlines. Yet out at sea, it unleashed something astonishing.
Average waves in the core of the storm topped 19 metres. Embedded within that chaos, a handful of giants are estimated to have climbed to around 35 metres from trough to crest. For reference, that is higher than many lighthouse towers and roughly the height of a mid-rise city block.
These waves travelled about 24,000 kilometres, circling from the North Pacific, through the Drake Passage, and into the tropical Atlantic.
On the way, long-period swells from Eddie arrived at Hawaii and California. For surfers, it was a once-in-a-decade spectacle, powering legendary big-wave competitions like the Eddie Aikau Invitational. For scientists, it was something else entirely: the clearest real-world test yet of how far and how efficiently storm energy can travel through the oceans.
Researchers led by French oceanographer Fabrice Ardhuin later showed that Eddie ranked among the most intense storms recorded in the last 34 years. Its waves rivalled, and in some cases exceeded, those from the infamous 2014 storm Hercules, which battered coasts from Morocco to Ireland.
What satellites are suddenly revealing about giant waves
Oceanographers have long relied on numerical models to guess the height and energy of waves, especially in remote parts of the sea. Until recently, there was a problem: direct measurements in mid-ocean were rare, and satellite data were too coarse to capture the full picture of extreme swells.
That changed with SWOT — the Surface Water and Ocean Topography mission, a joint project by NASA and the French space agency CNES. Launched to better track lakes, rivers and ocean currents, SWOT has also become a game-changer for wave science.
How SWOT measures monster waves
SWOT uses radar interferometry to map the surface of the ocean with fine detail. From these maps, scientists can extract the height and length of ocean waves over huge areas.
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- It can detect long swells with wavelengths above 500 metres.
- It measures wave height even thousands of kilometres from the storm that generated them.
- It tracks the direction and spacing of waves with unprecedented accuracy.
In December 2024, as Eddie’s swells spread across the Pacific, SWOT passed overhead. The data it recorded have shaken assumptions that underpinned decades of coastal risk assessments.
For the first time, scientists confirmed the presence of very long-period waves — up to 30 seconds between crests — carrying much more focused energy than classic models suggested.
Earlier empirical formulas had suggested that the longest waves carried about twenty times more energy than they really do when looked at in bulk. The new satellite data show something subtler: the energy is concentrated into a smaller number of dominant waves, rather than evenly spread across the whole sea state.
One researcher compared it to a boxer who wins not by throwing dozens of light jabs but by landing a few heavyweight punches. Most waves in the train are big; a select few are devastating.
A new way of thinking about wave spectra
The findings, published in 2025 in the journal Proceedings of the National Academy of Sciences, go beyond one storm. They support a new “spectral” representation of extreme waves that takes non-linear interactions more seriously.
In simple terms, short waves and long swells do not behave like separate, polite guests at a party. They interact. They exchange energy. Under some conditions, those interactions can fatten the tail of the wave spectrum, feeding extra power into a handful of bigger crests.
This refined view helps explain why a coastlines can suddenly see a cluster of abnormally high waves even when the average sea state looks manageable.
What more energetic seas mean for coasts
These insights matter far from the open ocean. Long-period swells are particularly efficient at moving sand, attacking cliffs and rattling port infrastructure. They also reach beaches that may lie thousands of kilometres from the original storm.
Coastal engineers care less about the typical wave and more about the worst few that arrive during a storm window. The new satellite-backed models sharpen that picture, changing how risk is calculated for harbours, seawalls and offshore platforms.
Hidden risks for coastal communities
A set of towering waves that arrive on an otherwise pleasant winter day can still cause trouble. Long swells do not always look dangerous from the shore until they break.
| Wave characteristic | Typical effect on coasts |
|---|---|
| High, short-period waves | Violent but localised breaking; surface damage to structures |
| Long-period swells | Deep energy penetration, strong rip currents, enhanced erosion |
| Clusters of extreme waves | Overtopping of defences, harbour damage, risk to people on shore |
Port authorities may need to rethink how they schedule ship movements during distant storms. Beachside communities might face more frequent “sunny day” flooding, when swells combine with high tides to push water over the berms even without local wind.
As sea level rises, long swells ride on a higher baseline, making overtopping and erosion more likely, even if storms do not get stronger.
Researchers are cautious about drawing straight lines between climate change and individual storms like Eddie. Still, simulations suggest that a warmer atmosphere can store more moisture and energy, influencing the frequency and tracks of intense low-pressure systems over the oceans. Local seabed topography, coral reefs and sandbanks will then shape how that energy finally hits the shore.
From satellites to building codes
The Eddie event is already feeding into practical decisions. With access to more accurate sea-state statistics, engineers can refine design standards for offshore wind farms, oil platforms and data cables. These structures are expected to survive rare but extreme loads over several decades.
Better wave spectra also help seismologists. Large waves flex the ocean floor and can generate tiny “microseisms” picked up by land-based seismometers. Understanding where and how those waves form and propagate makes it easier to separate this ocean noise from signals linked to earthquakes.
Key terms that shape the debate
A few concepts sit at the heart of this new research:
- Swell period: The time between two consecutive wave crests. Longer periods mean swells that feel smoother but carry energy deeper into the water column.
- Wave spectrum: A way of describing the sea surface as a mix of many wave components of different lengths and directions, rather than a single uniform train.
- Non-linear interaction: The process by which waves exchange energy and alter each other’s height and direction, especially during strong storms.
For people who live or work by the sea, one simple rule follows: a small number of waves often does most of the damage. Forecast tools that focus only on “significant wave height” — a kind of average of the tallest waves — can miss this clustering effect. New satellite-backed models are starting to plug that gap.
As missions like SWOT continue to scan the oceans, more events like Eddie will be captured in fine detail. Each one adds a data point to a rapidly evolving picture of how energy moves through a warming, changing ocean, and how those distant walls of water can quietly reshape coasts half a world away.
Originally posted 2026-03-11 21:20:50.