Why the northeast storm surge was so strong and what it reveals about the coming El Niño winter

As a powerful nor’easter storm 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 even have uncovered a wreck more than a century old.

Atlantic City, New Jersey, experienced its highest water levels since superstorm Sandy in 2012, as the storm surge swept away homes and vehicles and eroded protective beach dunes.

I study storm systems. People may be wondering if the northeast flooding is a prelude to what to expect as a strong El Niño continues to develop this winter and sea levels rise in the future. To understand the risks, let’s break down what caused the waters to rise so high.

The storm surge

Several factors are contributing to the high water levels and have combined to worsen flooding across the Northeast.

Storm surge is the accumulation of water caused by strong winds pushing water towards the shore. As the nor’easter began to take shape, strong winds began to push water hundreds of miles from the Atlantic toward the coast. As the storm intensified and its pressure decreased, the winds became stronger and this surge of water intensified.

Four basic factors determine the height of the waves at a given location: the strength of the land wind, the size of the storm, the shape of the coastline, and the depth of the ocean.

The September 2026 flood was highest where water was directed into shallow bays and coves. In these areas, the thrust of the water is concentrated in a small area with no place to go but onto land. Some of the largest surges in the Northeast occurred in New Jersey’s Raritan Bay and Delaware Bay.

The slow northeast movement along the East Coast resulted in a large and sustained surge.

High tides increase the risk of flooding

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

The heaviest flooding occurs when the peak of the storm surge coincides with high tide. Even worse is when high tides are higher than normal, such as around the full moon. The gravitational pull of the Moon and Sun combines around a full moon to make tides larger. This is what happened at the height of the northeast.

Additionally, the northeast’s long duration allowed flooding to occur during several high tides, leading to repeated rounds of coastal flooding.

The role of sea level rise

Another important factor in flooding is sea level rise. Sea level rise is due to global warming. This melts glaciers, sending more water into the oceans and causing the ocean to physically expand.

Sea level rise is occurring more rapidly in some parts of the U.S. East Coast than in others, primarily due to what is called post-glacial rebound. The weight of the Laurentide Ice Sheet that covered large parts of North America thousands of years ago pushed up the land beneath it, while also causing the land around its edges, including along the mid-Atlantic coast, to rise. As the ice melted, the edges that had risen slowly sank again.

In Atlantic City, sea levels are rising at a rate of about 50 millimeters every ten years. A few inches can mean the difference between water staying out of the house or flowing into it. Even if northeast storms don’t get stronger in the future, they will become more damaging because sea levels are already higher and more places will be flooded.

Other things to come this El Niño winter?

With one of the strongest El Niño events in recent memory already affecting weather patterns around the world, is this start to the season a sign of things to come? It’s hard to say.

A study found that strong northeast winds along the East Coast are more likely during El Niño years.

Seasonal forecasts from computer models suggest an increased likelihood of above-normal precipitation along the East Coast during winter. This suggests that moisture-laden storms accompanied by heavy precipitation may be more likely to move up the coast with devastating storm surges.

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

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, especially if you are in a flood-prone area. Have an emergency supply kit and make sure its contents are refreshed.

If a major storm threatens, pay attention to weather forecasts from reliable sources and listen to the advice of emergency managers in your community to keep everyone safe.