The best months to visit Ajaccio are May, June, and September. The weather is warm and sunny, the sea is swimmable, the roads are manageable, and prices are lower than in July and August. In high summer the city fills with French tourists from the mainland and ferries book up weeks ahead.
July and August are hot — regularly above 30°C — and crowded. If you are coming in summer, book accommodation and ferry crossings early and accept that popular beaches will be busy.
Winter is mild by French standards (10–15°C in January), the city is quiet, and many smaller restaurants close. It is a reasonable time to visit if you want the place to yourself, though some services run on reduced schedules.
The Fête de la Saint-Napoléon (15 August) is celebrated with particular enthusiasm here: fireworks over the port and a general air of civic pride.