Joinville sits in the humid subtropical zone — warm and rainy in summer, mild and drier in winter. December to March is the hottest, most humid period, often with afternoon thunderstorms. June to August is the most comfortable season for sightseeing, though nights can be cool by Brazilian standards.
The two big calendar fixtures are the Festival de Dança in late July, when the entire city is dance-mad and accommodation is hard to find, and the Oktoberfest in October. The Festa das Flores in November is a third draw.