(Bloomberg) -- New York City and the eastern US braced Sunday for severe thunderstorms as a creeping weather front drags across the region and raises the risk of flooding from Vermont to North Carolina. 

The slow-moving line of showers was crossing the region starting Sunday afternoon, with as much as 4 inches (10 centimeters) of rain possible in some locations, the National Weather Service said. Flood watches were issued for the Washington-Baltimore region as well as areas of New York, New Jersey, Pennsylvania, Connecticut, New Hampshire and Vermont. 

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.

Rain may fall at rates of 2 inches per hour through early Monday in New York, said Bryan Ramsey, a National Weather Service meteorologist in Upton, New York. Because the storm is moving so slowly, accumulations may pile up in harder-hit areas. 

“We are going to be looking at some very heavy rainfall, this will include the I-95 corridor,” said Andrew Orrison, a forecaster with the US Weather Prediction Center. “In general, the region up here has been wet, so we are looking at significant impacts.” 

Areas of flooding were already being reported west of Philadelphia, where the rain began falling late Sunday afternoon, the Philadelphia Inquirer reported. In Baltimore, rain was falling at 1 to 3 inches per hour, the Baltimore Sun reported.

The New York City Emergency Management Department urged New Yorkers to prepare for heavy rain through Sunday night that could flood basement apartments and create dangerous travel conditions. 

While about 80 million people are in the storm’s path, the highest rain totals are expected across portions of the Northeast and New England, forecasts predict, with some seeing a month’s worth of moisture in just a few hours. Because the front is moving slowly, the bands of rain and flooding threat could linger until Monday morning.

Nearly 400 flights have been canceled at New York’s LaGuardia and John F. Kennedy airports, and more than 170 at Newark, according to FlightAware, an airline tracking company. 

(Updates with Orange County state of emergency in third paragraph.)

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