Dangerous flash floods stranded motorists and left roadways under water. Some outdoor activities were canceled as communities scurried to keep pace with the rising waters.

The agency predicted rain would fall at a rate of 1 to 2 inches per hour, potentially overwhelming small creeks and streams, streets, highways and underpasses, as well as other poor drainage and low-lying areas.

A "considerable" flash flood warning has been issued in Boston as heavy, life-threatening rain pounds the city and areas to the south.