Summer is peak season and Dubrovnik feels it. July and August bring warm seas and long days but also cruise-ship crowds that can overwhelm the old town. The Dubrovnik Summer Festival runs from mid-July to late August, filling Renaissance courtyards and fortresses with theatre, music, and dance performances.
May, June, and September are the sweet spot. The weather is warm, the sea is swimmable from late May onward, and the old town is far more manageable. Prices drop from the summer highs.
Autumn lingers on the Adriatic coast. Swimming is often comfortable into early October, though the bura winds from the Dinaric Alps can pick up in late autumn and disrupt ferries and flights.
Winter is the quiet season. From November through March, many restaurants and attractions operate on reduced hours or close entirely. Accommodation is cheaper, and you may have the city walls nearly to yourself, but the smaller towns and islands around Dubrovnik largely shut down. Spring can be rainy, and the sea stays cold until mid-May.