Costa del Sol: Annual Weather Averages. August is the hottest month in Costa del Sol with an average temperature of 26°C (79°F) and the coldest is January at 12°C (54°F) with the most daily sunshine hours at 11 in August. The wettest month is November with an average of 115mm of rain. The best month to swim in the sea is in August when the average sea temperature is 23°C (73°F).