Other facts from our historical weather data: Which is the warmest month in Mullion? August has an average maximum temperature of 20°C (68°F) and is the warmest month of the year. Which is the coldest month in Mullion? The coldest month is February with an average maximum temperature of 11°C (52°F). Which is the wettest month in Mullion? November tops the wettest month list with 103mm (4.1 in) of rainfall. Which is the driest month in Mullion? May is the driest month with 61mm (2.4 in) of precipitation. Which is the sunniest month in Mullion? May is the sunniest month with an average of 222 hours of sunshine. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.