The weather in Cozumel is excellent. On average, you’ll enjoy sunny, slightly humid but breezy weather in the 80s (F) during the day – high 80s (F) from April to October, and lower 80s from November to March (Range from 28-32 Celsius). At night, it (usually) cools off but rarely goes below 70F (21C). (Winter months? Bring a fleece and jeans. And then likely note later that you didn’t need them… )
Like most tropical areas, there is always a chance for brief rain shower – sometimes hard rain, but usually it passes quickly – bring a light rain jacket.
The rainy season is from typically from mid-late August through early October. This corresponds with the regional hurricane season in the Western Atlantic and Caribbean, so rain is more common, with higher totals. Rarely, though, does it rain for full days, unless a storm is moving through. Mosquitoes are more common during this time.