Early summer heat will continue through the weekend. After that, temperatures next week will dip somewhat but stay slightly above normal.
This weekend, most regions will come under the influence of high pressure, sending temperatures higher. Clear skies will also bring large temperature swings between day and night. With no clouds overnight to trap heat from the ground, radiative cooling will be strong and temperatures are expected to drop.
On Saturday the 18th, morning lows are expected at 8–14 C, with afternoon highs at 18–28 C. Forecast lows and highs for major cities are 10 C and 27 C in Seoul, 10 C and 23 C in Incheon, 11 C and 27 C in Daejeon, 14 C and 25 C in Gwangju, 13 C and 25 C in Daegu, 13 C and 23 C in Ulsan, and 14 C and 20 C in Busan.
On Sunday the 19th, morning lows will be 9–14 C and afternoon highs 20–29 C, topping 20 C nationwide. As the pressure pattern shifts, next week likely will not be as warm as the weekend.
From the 20th to the 26th, temperatures are expected to range from 7–14 C in the morning to 17–26 C in the afternoon. That is somewhat lower than this weekend, but similar to or slightly above normal temperatures (lows 6–11 C, highs 18–23 C).
Meanwhile, rain will begin on Jeju and the South Jeolla coast from the early morning of the 17th, and in the rest of the southern regions and North and South Chungcheong from the morning. A low is passing south of Jeju. Rain will taper off in Chungcheong on the night of the 17th, but is expected to continue in North Jeolla and southern North Gyeongsang into the early morning of the 18th, in South Jeolla and South Gyeongsang in the morning, and on Jeju through the afternoon.
Expected rainfall amounts are 30–100 mm on Jeju (except the north; up to 150 mm or more in the mountains; up to 120 mm or more in the mid-slope areas), 20–60 mm in Gwangju, South Jeolla, western South Gyeongsang, and northern Jeju, 10–40 mm in Busan, Ulsan, central South Gyeongsang, and eastern South Gyeongsang, 5–30 mm in North Jeolla, 5–20 mm in Daegu and southern North Gyeongsang, around 5 mm in central and northern North Gyeongsang, Ulleung Island, and Dokdo, and under 5 mm in Chungcheong.
Heavy rain advisories may be issued for Jeju, where significant rainfall is expected, and strong waves are likely along the low's path in the Jeju sea, the far southern sea, and the far eastern sea, so caution is advised.