The hottest period in Korea is from late July to early August. During this time, the temperature can soar to 40 degrees Celsius, (104 °F), with overnight temperatures extending past 25 degrees Celsius (77 °F), producing humid tropical nights.
The best season to visit Korea
Considering both the cold winter and the hot and rainy summer, the best times to visit South Korea are spring and autumn, especially the months of May and October. The latter can be preferred because it's less rainy (and it's outside the so-called yellow dust season). Moreover, in autumn, you can admire the fall foliage in national parks.
As previously mentioned, the sea is warm enough for swimming from July to September, especially in the center-south.
What to pack
In winter: for Seoul and the center-north, Bring warm clothing, such as a down jacket, gloves, a scarp, and a hat.
In summer: Bring light clothing of natural fibers, a light raincoat or umbrella, a scarp for the wind, and a light sweatshirt for air-conditioned places.
* In the spring when there is a lot of fine dust in Korea, you will see a lot of people wearing masks. It is recommended to bring a mask or wear a mask after purchasing it in Korea.
* Also, it is essential to wear a mask unconditionally in the corona era these days.