Weather conditions on Cozumel are more extreme than you might expect on a tropical island. Nortes -- winds from the north -- blow through in December, churning the sea and making air and water temperature drop. If you visit during this time, bring a shawl or jacket for the chilly 65° evenings. Summers, on the other hand, can be beastly hot and humid. The windward side is calmer in winter than the leeward side, and the interior is warmer than the coast.