With rain coming down so fast, storm drains couldn't handle the deluge of water. On Interstate 93 in Quincy, all were lanes closed at one point because of extreme flooding during rush hour. At least five cars were stuck on the highway until the water receded.

A "considerable" flash flood warning has been issued in Boston as heavy, life-threatening rain pounds the city and areas to the south. Two to 4 inches of rain has fallen so far. Rainfall rates are reaching up to 2 inches per hour.

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.