Gran Canaria: Annual Weather Averages. August is the hottest month in Gran Canaria with an average temperature of 24°C (75°F) and the coldest is January at 18°C (64°F) with the most daily sunshine hours at 10 in August. The wettest month is December with an average of 31mm of rain. The best month to swim in the sea is in September when the average sea temperature is 23°C (73°F).