Climate in Northern Japan
Northern Japan's coldest month of the year is usually January where the temperates often hover between 5˚C and 10˚C. January is also the driest month of the year with an average precipitation just below 50mm. The hottest month of the year comes in August where temperatures become as high as 25-30˚C. The majority of the precipitation falls in the summer and fall with the two largest amounts of it falling in June and September with almost 190mm in these months. The location of Japan being next to a major ocean makes it have very warm weather, however, it ends up precipitating much more in the summer than in the winter.
Climate graph of Tokyo, Japan
Climate of South Korea
Although South Korea has significantly colder temperatures year round, January is still the coldest month with temperatures that go as low as -5˚C. It is again the driest month in the entire year with as little as 20mm of precipitation. The warmest month of the year is again August with an average temperature of about 25˚C. It is also the wettest month of the year in terms of precipitation where around 390mm will fall. The climate of South Korea is very similar to Japans with how it is affected by it being so close to the ocean, however, because it is more towards the inland, the temperatures and precipitation are a little more extreme.