Late May to mid-June and September are the sweet spots: warm enough for swimming, calm seas, and the high-season crowds yet to arrive or already gone. July and August are hot (often above 30°C) and busy, but also when the town comes properly to life with concerts in the fortresses.
The Šibenik International Children's Festival in late June and early July fills the squares with street theatre and music. The Off Jazz & Blues Festival in August brings acts to St Michael's Fortress, where the stage faces out across the archipelago. Winter is quiet, mild and damp; many waterfront restaurants close.