The Seychelles has two monsoon seasons. The northwest monsoon (November to April) brings calmer seas, lighter winds, and the best conditions for diving and snorkelling — this is peak season, and prices reflect it. The southeast trade winds (May to September) bring cooler temperatures and rougher seas, particularly on the south and west coasts. Anse Lazio, on the northwest, is more sheltered in the southeast monsoon and can be swimmable when the south coast is not.
The Vallée de Mai is worth visiting year-round. The black parrots are most active and most visible in the fruiting season (roughly June to August), when the coco de mer nuts ripen. Whale sharks pass through Seychelles waters from October to March, and the dive sites around Praslin are at their best in this period.