So what’s the best way to blow these precious last days of short-sleeved weather? Those with cars should grab a windbreaker and jet up — like, now! — to City Island. After you’ve indulged in the obligatory fried lobster tails, frog legs, and mai tais on the waterfront deck of the inimitable Johnny’s Famous Reef Restaurant, board the Riptide III, leaving at 6:30 p.m., for seafood straight out of the water rather than out of the deep fryer.