Deadly flooding swept through the lower Hudson River Valley north of New York City, snarling commuter travel as a slow-moving weather front made its way through the US Northeast promising more devastation.

As much as 8.12 inches (20.6 centimeters) of rain fell at the US Military Academy at West Point through 6 a.m. Monday as a flash flood emergency unfolded in the region the prior day, said Andrew Orrison, a forecaster with the US Weather Prediction Center. At least one person died, according to the Associated Press, with social media showing many roads were flooded or blocked by debris.

The flooding will likely hit eastern New York and Vermont hardest because those regions have had a lot of rain in recent weeks leaving soils saturated, according to Orrison.

A slow-moving cold front supported by a larger upper level trough of low pressure, unusual for this time of year, has been able to tap into a steady flow of moisture off the Atlantic made worse by unusually high temperatures in the ocean, Orrison said. “The warm ocean helps contribute additional moisture around this front,” he added.

The world’s oceans have seen record warming through 2023, which many scientists attribute mainly to climate change, as well as other factors. In a warming world, brought on by rising greenhouse gases, the atmosphere can hold more water, which has caused more extreme flooding. 

Trains on Metro-North Railroad’s Hudson Line have been stopped between Croton-Harmon and Poughkeepsie to let crews repair tracks and remove downed trees, according to the commuter-rail agency’s website. Service on the Wassaic Branch has been suspended. Amtrak temporarily halted travel between New York and Albany due to track damage, its website said.

In the air, some 2,435 flights have been cancelled Sunday and Monday with the majority of those occurring at New York City area airports, as well as Boston, according to FlightAware, an airline tracking company.

“The immediate concern for today is the heavy rain and the flooding across the Northeast, especially areas north of New York City,” Orrison said. “The worst conditions should be today and tonight.”

New York Governor Kathy Hochul declared a state of emergency for Orange County, New York, after excessive rains caused flash flooding, according to a statement.

Rivers and streams have swelled their banks due to the rain. The Housatonic River rose by 6 feet in some places of Connecticut in the last day, data from the National Weather Service show.

Flood watches and warnings reach from northern New Jersey to western Maine, and rainfall alerts have been posted in Quebec by Environment and Climate Change Canada. The storm is a combination of several weather systems.