In June, the weather in Cayo Guillermo is typically hot. Average daily high temperature in June is about 28 degrees above zero. On average, Cayo Guillermo has 16 rainy, 7 sunny, 4 partly cloudy, and 3 cloudy days in June. The rains are usually heavy. June as well as July, August, September, and October is considered the most uncomfortable time to visit Cayo Guillermo.