Other facts from our historical weather data: Which is the warmest month in Londonderry? July has an average maximum temperature of 19°C (66°F) and is the warmest month of the year. Which is the coldest month in Londonderry? The coldest month is January with an average maximum temperature of 9°C (48°F). Which is the wettest month in Londonderry? August tops the wettest month list with 108mm (4.3 in) of rainfall. Which is the driest month in Londonderry? March is the driest month with 86mm (3.4 in) of precipitation. Which is the sunniest month in Londonderry? May is the sunniest month with an average of 203 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.