Ilhabela's climate is warm and humid year-round, but the seasons shape the experience significantly. Summer — roughly December through March — brings intense heat, higher humidity, heavy afternoon thunderstorms, and enormous crowds. São Paulo residents pour onto the island for the holiday season, prices spike, and the ferry queue for cars can mean hours of waiting. If you enjoy a buzzing beach-town atmosphere and don't mind the rain, it's a perfectly good time to visit; just book well ahead.
The quieter months of April through June offer a gentler rhythm: fewer people, lower prices, and still-warm weather perfect for hiking and waterfall swimming. July brings the Semana Internacional de Vela, the island's most celebrated annual event, when hundreds of sailing boats fill the channel and the waterfront turns festive. It draws large crowds but of a different, more relaxed kind than the summer mass tourism. August through November is the driest period and arguably the best time to tackle the longer trails — the forest paths are drier, the waterfalls still flowing from winter rains, and the island is at its most accessible without the crush of high season.