I guess humid is relative lol. It’s more in August where fronts come to die. Almost any wind direction brings higher humidity off those SSTs.
I’ve been to MVY several times. Real cool place. ACK on my list, but maybe one day I’ll afford it haha.
On the Cape we’ve typically rented a house in the Brewster area on one of the kettle ponds. Get some freshwater kayaking, fishing, and swimming in addition to the beaches. We go with my in-laws who I get along with very well. It’s just a nice time. You have the rail trails too for biking.