As a powerful nor’easter hit the U.S. Atlantic Coast in late September 2026, the ocean poured into coastal neighborhoods from North Carolina to New York. Water from the storm surge and heavy rain filled streets and surrounded homes as near-hurricane-force winds knocked out power. It may have even uncovered a shipwreck more than a century old.

Atlantic City, New Jersey, saw its highest water level since Superstorm Sandy in 2012, as the storm surge washed into houses and vehicles and eroded protective beach dunes.

I study storm systems. People may be wondering if the nor’easter flooding is a prelude for what to expect as a strong El Niño continues to build this winter and as sea level rises in the future. To understand the risks, let’s break down what caused the water to rise so high.

Several factors go into high water levels, and they combined to worsen flooding during the nor’easter.

Storm surge is the piling up of water caused by strong winds pushing water onshore. As the nor’easter began to take shape, gale-force winds began pushing water over hundreds of miles of the Atlantic toward the coast. As the storm strengthened and its pressure dropped, the winds grew stronger and this push of water intensified.

There are four basic factors that determine the surge height at any given location: the strength of the onshore wind, the size of the storm, the shape of the coastline and the depth of the ocean.

The September 2026 surge was highest where the water was directed into shallow bays and inlets. In those areas, the push of water becomes concentrated into a small area with nowhere to go but onto land. Some of the largest surges during the nor’easter were in Raritan Bay in New Jersey and Delaware Bay.

The slow movement of the nor’easter up the East Coast resulted in a large, sustained surge.

Inundation – the actual water level above the ground – depends on both the storm surge and the tide.

The greatest flooding occurs when the peak storm surge coincides with high tide. Worse yet is when the high tides are higher than normal, such as around a full moon. The gravitational pull of both the Moon and the Sun combine around a full moon to make the tides larger. That’s what happened during the height of the nor’easter.

Additionally, the long duration of the nor’easter allowed inundation to occur over multiple high tides, resulting in repeated rounds of coastal flooding.

Another important factor for inundation is sea-level rise. Sea-level rise is occurring because the planet is warming. That melts glaciers, sending more water into the oceans, and causes the ocean to physically expand.

Sea-level rise is occurring faster in parts of the U.S. East Coast compared with other areas, primarily due to something called post-glacial rebound. The weight of the Laurentide ice sheet that covered large parts of North America thousands of years ago pushed down the land below it, while causing the land around its edges to rise – including along the mid-Atlantic seaboard. As the ice melted, those edges that had lifted slowly sank again.

In Atlantic City, sea level is rising at a rate of about 2 inches (50 millimeters) every decade. A couple of inches can mean the difference between water staying out of one’s house or pouring in. Even if nor’easters don’t become stronger in the future, they will become more damaging because sea level is already higher, and more places will experience flooding.

With one of the strongest El Niños in recent memory already affecting weather patterns around the world, is this early-season nor’easter a sign of things to come? It’s difficult to say.

One study found that strong nor’easters along the East Coast are more likely during El Niño years.

Computer model seasonal forecasts suggest an increased chance of above-normal precipitation along the East Coast during the winter. This suggests moisture-laden storms with heavy precipitation may be more likely to move up the coast with damaging storm surges.

However, every El Niño is different, and there are few past El Niños close to the strength expected this time to compare with.

The best advice this El Niño winter is to be proactive in preparing and monitoring the weather. Check your insurance policies to understand your coverage, particularly if you are in a flood-prone area. Have an emergency supply kit and make sure its contents are refreshed.

Should a big storm threaten, pay attention to the weather forecast from trusted sources and listen to the advice of your community’s emergency managers to keep everyone safe.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Brian Tang, University at Albany, State University of New York

Read more:
2026’s El Niño is shaping up to be a doozy – it’s already affecting global shipping, fish behavior and heat

Galápagos corals show El Niño events are more extreme now than in past 1,000 years – here’s how my team made the discovery

Sea level doesn’t rise at the same rate everywhere – we mapped where Antarctica’s ice melt would have the biggest impact

Brian Tang receives funding from the National Science Foundation, the National Aeronautics and Space Administration, and the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography at UC San Diego.