Other facts from our historical weather data: Which months have the greatest rainfall in Port William? Most rainfall (rainy season) is seen in October and November. Which is the warmest month in Port William? August has an average maximum temperature of 17°C (63°F) and is the warmest month of the year. Which is the coldest month in Port William? The coldest month is February with an average maximum temperature of 9°C (48°F). Which is the wettest month in Port William? November tops the wettest month list with 155mm (6.1 in) of rainfall. Which is the driest month in Port William? May is the driest month with 76mm (3 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.