Summer in South Korea (from June to August) is usually hot and humid with a lot of rainfall during the rainy season of the East Asian monsoon (Changma). About 60 percent of precipitation falls during this season.
I can attest to the hot summers as I was there in June/July 2001 and again in June of 2016 but the next time I go, I plan to go in May 2024.
I loved our time in Korea. I felt so bad when your camera was ruined from the intense rain we walked through. I cannot wait to go back!!!!!