The best months are October to March. The monsoon retreats in September or October, leaving the island green and the waterways full but manageable. By November the weather is dry and clear, with cool nights and warm days — ideal for cycling between satras. The Raas Leela festival in mid-November is the single best reason to time a visit.
December and January are cooler still, and the river levels drop to reveal more of the sandbanks and beaches. This is also prime birdwatching season, when wintering migrants arrive from Central Asia and Siberia. February is the Mishing festival of Ali-Ai-Ligang.
April to September is the monsoon. The island partially floods — the satellite ferries are suspended, some roads become impassable, and several satras sit nearly surrounded by water. Experienced travellers who don't mind the damp and the disruption sometimes visit in June or July when the island takes on a different character, but this is not recommended for a first visit. The heat in April and May before the rains break is also considerable.