May, June, and September are the best months — mild temperatures (15–20 °C), longer daylight, and the lowest chance of rain. July and August are the warmest but also the wettest and busiest. Cork has a maritime climate; it rains often year-round and you should expect at least one wet day per week even in summer.
The Cork Jazz Festival in late October is the city's most famous annual event, drawing big-name musicians and turning every pub into a venue for the weekend. The Midsummer Festival in June and the Cork Film Festival in November are also worth timing a visit around.