WESTPORT — Periodic downpours and flash flooding disrupted Monday afternoon’s commute on local roads and rails.

Pooling water flowed across stretches of town streets after heavy rain late Monday afternoon and early evening, while a flash flood warning was extended for the town throughout the afternoon into evening by the National Weather Service.

Meanwhile, the rain flooded Metro-North Railroad tracks heading north from New York, forcing “combined trains, delays and crowding conditions” for evening New Haven Line commuters heading out of Grand Central Terminal, according to a statement from the railroad.

Compounding the treacherous weather is a “Severe Thunderstorm Watch” issued though 10 p.m. Monday by the weather service.

A “Flood Advisory” for “low-lying and poor-drainage areas” remains in effect until 8:30 p.m. Monday, as more heavy rain is expected to fall.

“Showers and thunderstorms likely, mainly before midnight,” according to the NWS forecast. “Some storms could be severe, with damaging winds, heavy rain and frequent lightning.”

While significant power outages were reported Monday evening in some area towns — notably, New Canaan, with more than 400 and Norwalk, more than 250 — Westport had “fewer than 2” of its more than 12,600 customers without power as of 7 p.m., according to the utility, Eversource.

Monday’s stormy weather is expected to clear the way for a heat wave gripping the region, with temperatures soaring into the 90s, from Tuesday through at least Sunday, the NWS predicts.