December through February is high summer in Santa Catarina — hot, humid, and busy with Brazilian beach holidaymakers. The water at Cabeçudas is at its warmest and the city feels at full speed. October sees the ten-day Marejada festival, the city's biggest annual event.
Spring (September to November) and autumn (March to May) are cooler and quieter, with pleasant temperatures and fewer crowds. Winter (June to August) is grey and cool — not unpleasant, but the beach is off the menu.