Itapema's summer is December through February — hot, sticky, and packed solid with Brazilians on holiday from Santa Catarina, Paraná, Rio Grande do Sul, and increasingly Argentina. Prices double, beaches fill, and traffic on the BR-101 backs up for kilometres on weekend afternoons. The town is at its most fun then if you do not mind crowds.
March, April, and November are the local sweet spot: the water is still warm, the beaches are quiet, and rates drop sharply. May to September is winter — cool, frequently rainy, and the sea is too cold for most swimmers, but this is when the tainha (mullet) run brings the fishing colony alive in late May and June. The Festa da Tainha, held annually in early June, is the calendar's biggest local event outside the summer season.