Due to its perfect location in the Indian Ocean, Mauritius has an ideal travel season that stretches from May to October. Enjoy these temperate, sunny days and cool nights (where a light cardigan may be required) and very little humidity. May is perfect if less crowds are your thing. July and August tend to get busy.
Humidity is relatively high, but not enough to make your vacation unpleasant. Cyclone season ends in February, leaving some moisture behind which dissipates over March and April, the latter month being the hottest time of year. A similar phenomenon is observed in November and December, as the island heads for its cyclone season once again. Despite the humidity, December is a very popular month for travel, so book in advance.
Cyclone season, so best avoided.