Pedestrians walk through the rain with umbrellas near Gwanghwamun Square in central Seoul on Friday. (Yonhap)

With heavy rainfall expected nationwide through Saturday, temperatures across South Korea are set to drop sharply from Sunday, ushering in chilly autumn conditions. Some regions may even experience their first snowfall of the season.

According to the Korea Meteorological Administration, Korea will see nationwide rain until Saturday as a low-pressure system from the west passes over the country.

While the rain will cease in most parts of the country from Saturday morning, the rain will likely continue along regions on the east coast until Saturday night as a high-pressure system expands above the Korean peninsula, bringing easterly winds. North Chungcheong Province and the Gyeongsang Provinces will see rain until Staurday afternoon.

The state weather agency added that the precipitation is expected to be unconventionally heavy for autumn rain.

From Friday to Saturday, the central region, consisting of the Greater Seoul area -- Seoul, Incheon and Gyeonggi Province -- Gangwon Province and the Chungcheong Provinces, may see rain ranging between 20 to 60 millimeters. Heavily hit regions may see a collective amount of rain of up to 80 mm. The east coast along Gangwon Province and its mountainous regions may see rain ranging between 50 to 100 mm, with heavily hit parts seeing rainfall of up to 120 mm. The Jeolla Provinces and Jeju Island may see rainfall reaching as much as 80 mm.

When asked about the reason behind this weekend’s heavy rainfall, KMA official Woo Jin-kyu told The Korea Herald that it was due to the low-pressure system being developed by the influence of a high-level jet stream and the high-pressure system.

“After this low-pressure system that’s passing over the Korean peninsula meets the low-level jet stream and cold northerly winds, rain clouds will be further developed, causing concentrated precipitation in Korea,” Woo continued.

The KMA added that the rain is adding to concerns about potential damage. This is because the earth and moon are currently at their closest point of the year, meaning the moon’s gravitational pull has a chance of strongly affecting the tides, raising sea levels. Due to low pressure passing through and rain falling, coastal lowlands could face flooding.

Strong winds are also expected over the weekend. On Friday, most areas will experience wind gusts of more than 55 kilometers per hour, while on Saturday, wind gusts are expected to range between 55 and 70 km/h.

A pedestrian walks through fountain grass at Gaetgol Ecological Park in Siheung, Gyeonggi Province during rainfall on Friday. (Yonhap)

After the rain, temperatures are expected to drop significantly as the cold air is brought into Korea from the north.

On Saturday, the average morning lows are expected to be as low as 16 degrees Celsius, while daytime highs are expected to reach as much as 21 C. Daytime temperatures will drop by 2 to 5 C between Friday and Saturday.

However, on Sunday, the morning lows are expected to reach as low as 10 C, while daytime highs are expected to reach 18 C. Daytime temperatures will drop by 3 to 10 C between Friday and Sunday.

According to the KMA, most parts of the country will not see temperatures above 19 C on Sunday, and morning lows are expected to be as low as 9 C.

In some parts of Gangwon Province, including its mountainous regions, morning lows may reach as low as 3 C, leading to ice formation on roads. The first snow of the year may be recorded in the province’s mountainous regions above 1,000 meters, though it would be a light amount.