BOSTON -- A slow-moving storm knocked out power for nearly 450,000 people across the Northeast Saturday, churning up water along the coast and prompting flood warnings for the state.

Rain is expected to become heavy Saturday night into Sunday, especially across the Merrimack River Valley, and pockets of flooding are expected along the coast. The flood warning will remain in effect through 3 p.m. Sunday, with individual waves likely to hit 25 feet during high tides.

The National Weather Service warned that inland rivers and streams may also be inundated by the persistent rainfall, and city streets could be clogged by accumulating storm water. Much of the state will be under a flood watch through Sunday night.

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"Some additional rain will fall Sunday night into Monday, so that total rainfall accumulations from the entire storm is likely 2 to 6 inches," said Storm Team 5 meteorologist Harvey Leonard.

The winds downed trees and power lines throughout New Jersey, New York, Pennsylvania and Connecticut. The New York City area and southern New Jersey were among the hardest hit, with wind gusts of up to 67 mph recorded and power cut to a combined 335,000 customers.

In Boston, winds were expected to reach 55 mph, along with rains of one to two inches. In northwestern Massachusetts, ice and up to five inches of snow was forecast.

Logan International Airport was hosting extra international aircraft Saturday as heavy rain and high winds created delays at John F. Kennedy International Airport in New York.

Massport spokesman Matthew Brelis said nine overseas flights had to stop in Boston because they no longer had the fuel to wait for clearance into Kennedy.

Residents in Plymouth kept a watchful eye on the coastline as the winds sent waves barreling toward their homes. For years, the beach has been slowly eroded by successive storms, and Saturday’s tempest threatened to further dissolve the barrier between the ocean and the waterfront property on Cape Cod Avenue.

The National Weather Service warned that high tides will likely cause erosion across the state’s coastline through Monday afternoon.