Heavy rain that inundated southwestern Connecticut early Thursday afternoon has triggered a flash flood watch for the region through Friday, with the National Weather Service warning more torrential downpours are possible Friday.

Westport police said Imperial Avenue had to be closed at its intersection with Bridge Street because of flooding early Thursday afternoon.

Police said a tree that fell on power lines cut service to traffic lights at the Sherwood Island Connector-Greens Farms Road intersection and also disrupted electric service to some nearby homes.

Unlike other area communities, where the downpour washed out power to thousands at the height of the storm, no serious outages were reported in Westport by Connecticut Light & Power.

In next-door Fairfield, however, sections of the Post Road were closed to through traffic, as were most of the viaducts under the local railroad tracks. Several side streets off the Post Road in downtown Fairfield also were either closed to traffic because of accumulated runoff several inches deep, or blocked by cars stalled in the ponding.

At one point Thursday afternoon, more than 2,700 Fairfield customers of the United Illuminating Co. lost power during the onslaught.