This story has been updated.
A Severe Thunderstorm Watch is now in effect for much of the Hudson Valley and all of Fairfield County as a band of storms moves from west to east.
The watch now covers Westchester, Fairfield, Rockland and Orange counties.
At 2:18 p.m. a severe thunderstorm was located near Tappan, moving northeast at 10 mph with 60 mph wind gusts, says the National Weather Service.
At 2:29 p.m., a severe thunderstorm, also with 60 mph winds, was located over Bedford, or near Mount Kisco, and is nearly stationary, the weather service reports.
The thunderstorm watch was added to include Fairfield County at 2:49 p.m. as the storms moved east.
The watch was issued for Orange County at 4:59 p.m.
Some locations that will experience flooding include Yonkers, Stamford, White Plains, New City, Ossining, New Canaan, Monsey, Nanuet, Tarrytown, Mount Kisco and Dobbs Ferry, the weather service said.
Urban and small stream flood advisories are in effect for Westchester, Rockland and southern Orange counties.
Torrential rainfall is occurring with the storms, and may lead to flash flooding, the weather service added, noting that residents should not drive vehicles through flooded roadways.
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