Other facts from our historical weather data: Which is the warmest month in Oldsum? 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 Oldsum? The coldest month is February with an average maximum temperature of 5°C (41°F). Which is the wettest month in Oldsum? August tops the wettest month list with 114mm (4.5 in) of rainfall. Which is the driest month in Oldsum? April is the driest month with 47mm (1.9 in) of precipitation. 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.