Cozumel Weather by Month: the Real Numbers

Cozumel is warm every single month. Average highs never drop below about 81F and never climb past about 90F, and the sea sits between roughly 79F and 85F all year, which means you will never need a wetsuit to snorkel and rarely want more than a thin one to dive. Nobody comes here and gets cold.

So the real variable is not temperature, it is water falling out of the sky and wind pushing the sea around. Roughly speaking: February through April is the dry, bright, flat-water stretch, May through August is hot and humid with short afternoon downpours, and September through October is the wet, cloudy, hurricane-peak window that is also the cheapest time to be here by a wide margin. November and December dry back out.

One thing the averages hide: winter can throw a norte, a north wind that kicks up chop for a day or two and pushes the dive boats to the sheltered southwest side. It is not a forecast you can plan around, just a thing that happens, and the southwest sites are where most of the good stuff is anyway.

People read 'rainy season' and picture a washed-out week. That is not how it works here. From roughly June through October the pattern is a hot, bright morning, clouds stacking up after lunch, then a hard downpour that empties the sky in half an hour and leaves everything steaming. You lose an afternoon hour, not a day. Boats mostly still run, beach clubs stay open, and the rain is warm.

The exception is September and October, when the systems get bigger and slower. September is the cloudiest month and averages the most rainy days of the year at about 15.9, and October dumps the most total water at around 5.6 inches. That is when you can genuinely lose a day, or when a storm sitting somewhere else in the Caribbean pauses the ferries and the dive boats for a stretch without ever hitting the island itself.

If you are diving or snorkeling, rain matters far less than you would think. The water is warm regardless, and surface rain does not touch visibility down on the reef. Wind is the thing that cancels a boat day, not rain.

Atlantic hurricane season officially runs June 1 through November 30, but the months that actually keep people watching the radar are September and October. A direct hit on Cozumel in any given year is uncommon, and the island is well drilled for it when it happens. The much more likely disruption is indirect: a storm anywhere in the region kicks up seas, and suddenly the Playa del Carmen ferry is cancelled and the dive boats are tied up for two or three days while the sky over you looks perfectly fine.

That is the risk you are actually pricing when you book September or October, and it is why those months are cheap. It is a reasonable trade if you buy travel insurance, keep the itinerary loose, and do not schedule the one thing you came for on your last day. It is a bad trade if this is a once-in-a-decade trip with a fixed plan. For how that risk stacks against crowds and price, see the best time to visit Cozumel.

The sea runs from about 79F in the late-winter low to about 85F at the late-summer peak. In practical terms: snorkelers never need anything, and most divers are comfortable in a 3mm shorty or skin year round, with a full 3mm being plenty for the coolest months if you run cold or are doing three tanks a day.

Visibility is the other number divers ask about, and Cozumel is spoiled here. It generally runs 80 to 100 feet or better all year, with the clearest stretch falling roughly December through May. Summer tends to bring the flattest, glassiest surface conditions. There is no bad season to dive here, which is the whole reason the island has the reputation it has, see the scuba diving guide for what that actually gets you.