Heavy rain will fall across the country on Wednesday the 20th.
The rain will begin before dawn on the 20th in the Chungcheong region and the south, then spread to other areas in the morning. It will continue through the afternoon on Thursday the 21st, and some rain will linger on the east coast and mountains of Gangwon and on Jeju into the evening on the 21st.
Forecast rainfall from the 20th to 21st is 50–100 mm on the east coast and mountains of Gangwon (over 150 mm in the Gangwon mountains at most); 30–80 mm in the Seoul metropolitan area, the five West Sea islands, inland Gangwon, Chungcheong, the northern East Sea coast of North Gyeongsang, the northeastern mountains of North Gyeongsang, and Jeju (over 120 mm at most in the Jeju mountains; over 100 mm at most on the Incheon, Gyeonggi, and northern Chungnam West Sea coasts, the five West Sea islands, and the mid-southern highlands of Jeju); 20–60 mm in Honam, Busan, Ulsan, South Gyeongsang, Daegu, and North Gyeongsang (excluding the northern East Sea coast and northeastern mountains), and Ulleungdo and Dokdo (over 80 mm at most on the southern coast of South Jeolla and the western part of the southern coast of South Gyeongsang); and 10–60 mm in northern Jeju.
Because the rain is associated with a low pressure system passing over Korea, there will be times when it pours. The heaviest rain is expected between late afternoon on the 20th and the morning of the 21st. During this period, central regions, the southern coast of South Jeolla, the western part of the southern coast of South Gyeongsang, and the mountains and mid-elevations of Jeju will see around 20–30 mm per hour.
Strong winds will accompany the rain. From the afternoon of the 20th, gusts around 55 kph nationwide (around 70 kph in the mountains) are expected, and from the night of the 20th, winds will be particularly strong on western and eastern Jeju and in the mountains, with gusts exceeding 70 kph (90 kph in the mountains).
Seas will be rough as well. Through the 20th, the moon's gravitational pull will raise tides above normal, and in the southern offshore waters of the West Sea, winds will blow very strongly at 30–60 kph (8–16 m/s) through the night of the 21st, with waves very high at 2–4 meters. Also, from the afternoon of the 20th in the central offshore West Sea, and from the morning of the 21st in the East Sea, South Sea, and Jeju Sea, conditions will become rough enough for high seas advisories to be issued.
With clouds and rain, the early heat will ease. Morning lows on the 20th will be 15–19 C, above normal, but daytime highs will stay at 18–23 C, near normal.
Forecast lows and highs in major cities are 19 C and 21 C in Seoul and Incheon; 17 C and 19 C in Daejeon; 19 C and 23 C in Gwangju Metropolitan City; 17 C and 20 C in Daegu and Ulsan; and 18 C and 21 C in Busan.