Cozumel has two seasons: a dry, breezy winter from November through April, and a wet, sticky summer from May through October. The dry season is when most people visit and prices peak around Christmas, New Year, and US spring break.
November to April brings warm sunny days (24–28°C), low humidity, and steady trade winds. Water temperatures hover around 25–26°C — cool enough for a 3mm wetsuit on long dives. This is the high season; book accommodation well in advance.
May to October is hotter (28–33°C), more humid, and prone to afternoon thunderstorms. Water temperatures climb to 28–29°C and visibility is often excellent. Hurricane season runs June through November, with the highest risk in September and October — Cozumel lies directly in the Caribbean hurricane belt and storms have closed the island for days at a time, as Wilma did in 2005.
Festivals worth timing a visit around: Carnaval, in the week before Ash Wednesday (usually February), is the island's biggest party, with parades through San Miguel and music in the main square. El Cedral, in late April or early May, is a five-day festival of bullfights, dances, and processions in the inland village of the same name — one of the oldest festivals in Mexico, dating from the 19th-century cholera epidemic.