So I go to Block island for a week around Memorial Day each year. Have to imagine the weather is similar to Martha’s Vineyard . There are some nice days, never expect temps to get above 70 but you can get some nice days in the 60s. However the bad days are complete garbage. Temps won’t get out of the lower 50s if it’s raining. Foggy too. Also it’s tough to get a perfect warm day at the beach since usually there will be wind too.
So overall I would say it’s a mixed bag with more bleh days than good.