WESTPORT — The continued threat of storms Sunday, possibly triggering heavy downpours and thunderstorms, has cancelled two civic events.

The CT United Ride, motorcyclists’ annual rolling tribute to victims and first responders of the Sept. 11, 2001, terror attacks, has been called off for the first time in two decades.

The event, which attracts hundreds of participants, had been scheduled to leave Westport from Sherwood Island State Park about 11:30 a.m. Sunday, and follow a route through eight other towns.

A Fall Festival, planned by the Japan Society of Fairfield County at 1 p.m. on Jesup Green, also has been cancelled because of concerns over possible severe weather.

A “Hazardous Weather Outlook” has been issued Sunday for southwestern Connecticut by the National Weather Service.

In addition to the likelihood of rain, with the sporadic threat of thunderstorms, the Sunday forecast also warms that “excessive” amounts of rainfall could trigger flash flooding.

Skies will remain cloudy Sunday, according to the NWS, with the daytime high temperature about 80 degrees.

On Monday, there remains a lesser chance for rain and thunderstorms during daytime, but the unsettled weather patterns are expected to leave the region by the evening.