Weather is probably a major factor when you plan your trip to Namsan, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually August and July with an average temp of 71°F, while the coldest months are January and December with an average of 29°F. The rainiest months in Namsan are July, August, June, and September, with each month seeing an average of 10 inches of rainfall.