Flash floods hit cities and towns south of Boston Thursday as historic rain brought traffic to a crawl and shut down part of I-93.

I-93 was essentially a river Thursday morning as torrential downpours dumped up to six inches of rain across eastern Massachusetts. As you probably heard from your phone's alert system screaming at you,

Boston, Quincy, Brockton, and other South Shore communities are under a flood watch until 9 a.m., according to the National Weather Service.