Cayo Guillermo: during the year, the average temperature throughout the year is around 27°C. The coldest period of the year is in the month of January where the temperature can drop to 24°C. The hottest month of the year is instead in July where the maximum temperature can reach 29°C. The water temperature, during the hottest months can reach an average of 28°C, during the coldest months it can drop to 22°C.