Rain has dampened activities at the Prescott Park Arts Festival this summer. According to organizers, the previous record for rained-out events in a single season was nine. This year, there have been a total of 18 rainouts.

“As an outdoor music festival, we’re really at the mercy of the weather,” festival director Ben Anderson said in a press release. “And while we prepare for rain, this summer was beyond anything like we’ve experienced before.”

But the weather has turned mostly pleasant in the waning days of summer, and Anderson has responded by booking one last show. The Shaw Brothers are playing a special benefit concert on Wednesday, Aug. 27, to close out the 34th annual festival. Like all summer shows at Prescott Park, the concert is free, with a suggested donation of $5 to $8.

Anderson said an Aug. 20 performance by singer-songwriter Livingston Taylor broke festival attendance records, drawing an estimated 6,000 people to Portsmouth’s waterfront park. He hopes the Shaw Brothers carry that momentum on Wednesday and help the festival recover from its soggy season.

After more than 40 years performing together, Rick and Ron Shaw have come to be recognized as New Hampshire’s musical ambassadors to the world. The identical twins were born and raised in the Granite State and attended the University of New Hampshire in the 1960s. Both Shaw brothers sing, play guitar and compose original songs, interspersing their traditional and contemporary folk tunes with humor, stories and poetry.

The Shaw Brothers have performed alongside such acts as Bob Hope, Ed McMahon, Joan Rivers, Johnny Mathis, Bill Cosby, Judy Collins, John Denver, Don McLean and Tommy Makem & Liam Clancy, among many others. They have played concerts all over the world, including shows in Japan, South Korea, China and Great Britain.

Wednesday’s show begins at 7 p.m. on the Prescott Park stage on Marcy Street. “The weather is now gorgeous and we’re happy to be able to extend the season,” Anderson said.