Heavy rain to drench nation Saturday, up to 100mm forecast for Greater Seoul

Rain is forecast to fall across the country through Saturday evening.

As of 5 p.m. Friday, rain was already falling across Jeju, the southern regions and parts of Chungcheong, with showers expected to reach the Greater Seoul area and Gangwon Province late at night.

The rain will spread nationwide and persist through Saturday evening in most areas, continuing into Saturday night in eastern Gyeonggi Province, Gangwon Province, North Chungcheong Province, central North Gyeongsang Province and northern North Gyeongsang Province. In Gangwon's mountain areas and along the East Sea coast, rain will linger through Sunday morning.

The rainfall is expected to be both intense and heavy.

From Friday night through Saturday morning, Jeju's mountain and mid-mountain areas will see bursts of more than 50mm per hour, while other parts of Jeju — excluding the mountains, mid-mountain zones and the northern area — will receive 30–50mm per hour, and northern Jeju 20–30mm per hour.

From early Saturday morning through the morning hours, the southern West Sea coast of South Jeolla Province, the South Sea coast and areas near Jirisan will see 30–50mm per hour, while the Greater Seoul area, Chungcheong, Gwangju, South Jeolla Province, North Jeolla Province, inland South Gyeongsang Province, Daegu and North Gyeongsang Province can expect 20–30mm per hour.

From Saturday morning through the afternoon, inland Gangwon Province will see 20–30mm per hour, with the same rate forecast for Gangwon's mountain areas and East Sea coast from Saturday morning through the night.

Total accumulated rainfall is forecast at 50–80mm for Jeju (with mid-mountain and mountain areas potentially exceeding 250mm); 50–100mm for Gangwon mountain areas, the Gangwon East Sea coast, Gwangju and South Jeolla Province (with central and northern Gangwon mountain areas and the central and northern Gangwon East Sea coast potentially topping 150mm, and southern Gangwon mountain areas, the southern Gangwon East Sea coast, the southern West Sea coast of South Jeolla Province, the South Sea coast and areas near Jirisan potentially exceeding 120mm); 30–100mm for the Greater Seoul area and northern South Chungcheong Province; and 30–80mm for inland Gangwon Province, Daejeon, Sejong, southern South Chungcheong Province, North Chungcheong Province, North Jeolla Province, Busan, Ulsan, South Gyeongsang Province, Daegu, North Gyeongsang Province, Ulleungdo and Dokdo (with the South Sea coast and areas near Jirisan potentially exceeding 100mm). The five West Sea islands will receive 20–60mm.

Heavy rain advisories are expected to be issued across multiple areas given the forecast for intense and abundant rainfall.

A heavy rain advisory is already in effect for Jeju's mountain areas and the mid-mountain zone of Seogwipo, while a preliminary heavy rain advisory has been issued for the rest of Jeju, the South Sea coast, and the central and northern Gangwon mountain areas and East Sea coast.

Strong winds will also sweep the country as a low-pressure system passes through.

Gusts exceeding 70 km/h (90 km/h in mountain areas) are expected along the Jeolla coast, the South Gyeongsang coast and Jeju early Saturday morning, and along the Gangwon East Sea coast from Saturday afternoon. The rest of the country will also see strong gusts of at least 55 km/h (70 km/h in mountain areas) on Saturday.

Rough seas are also expected. Starting Friday night in the southern outer waters of the West Sea, the waters south of Jeju and the outer eastern waters of the South Sea, winds of 30–60 km/h (8–16 m/s) and waves of 1.5–4.0 meters will spread to the West Sea, South Sea and waters around Jeju early Saturday morning, and to the East Sea by Saturday morning. Waves on the East Sea could reach a maximum of 5.0 meters or more between Saturday night and Sunday, and mariners are urged to exercise extreme caution.

Temperatures will drop as the rain moves in.

Saturday morning lows of 19–23 degrees Celsius will remain above seasonal norms, but afternoon highs of 22–29 C will fall below average.

For major cities on Saturday, morning lows and afternoon highs are forecast at 22 C and 25 C for Seoul, Incheon and Busan; 21 C and 26 C for Daejeon; 22 C and 26 C for Gwangju; 21 C and 29 C for Daegu; and 22 C and 27 C for Ulsan.

On Sunday, which marks the summer solstice, morning lows will range from 16 to 21 C and afternoon highs from 23 to 31 C.