Under the grand Rowes Wharf archway, the Boston Harbor Hotel’s 27th season of free waterfront music turns weeknights into a breezy harborside party of jazz, soul, and pop. Catch the Mark Erelli Band’s biweekly Friday residency or Thursday spotlights on rising local talent, with the harbor lapping behind the stage. Grab a lobster roll or a cocktail at the Sea Grille patio and settle in for one of the best free-music views in the city.