Seychelles is warm and tropical year-round — temperatures stay between 24°C and 32°C regardless of season, which makes it an unusual destination in that there's no truly bad time to visit. What changes is the wind, the sea state, and what's happening underwater.
April–May and October–November are the transition months between monsoons, and these are widely considered the best time to visit. Winds are light, the sea is calm, diving visibility can reach 30 metres, and whale sharks are present from September through November. The islands are at their most photogenic — lush after the rains, but not in the middle of any season's weather patterns.
December–March (northwest monsoon) brings warm, humid conditions and occasional heavy rain, particularly in December and January. The upside: seas around Mahé and Praslin are calmer during this period, the vegetation is lush and green, and La Digue and other southeastern beaches are sheltered. This is also peak tourist season — school holidays and Christmas/New Year bring high prices and full hotels. Book well ahead.
May–October (southeast trades) is drier and cooler (relatively — still warm). Seas on the eastern sides of the islands can get choppy, and some beaches become rough for swimming. The northwestern beaches of Mahé and Praslin, however, are at their best. This period is less crowded than the festive season.
Turtles nest on Seychelles beaches from October through February. The Vallée de Mai on Praslin is worth visiting at any time of year.