Although, Florianopolis does not face a conventional four season climate, yet it is better to exercise a little precaution depending on what month you are planning to visit.
There are no chilly winters as such but it is better to carry a sweater with you at all times from April to December as such.
April and May are quite pleasant with April being the driest month. January is generally the hottest month with temperature maintaining a 30 degree Celsius average. September is the wettest month. A windcheater, an umbrella, a sweater is enough to protect you from the rainfall or the winters.