Heavy rain to continue through Monday, bring hotter temperatures afterward

Heavy rain of around 40 millimeters (1.6 inches) per hour battered coastal areas of Gwangju on Sunday morning, while more than 250 millimeters of rain is forecast for parts of southern Korea through Monday.

As of 10 a.m. Sunday, heavy rain of 20 to 30 millimeters per hour was falling along the coast of South Jeolla and Gwangju and near Mount Jiri, according to the Korea Meteorological Administration (KMA). Sijong in Yeongam County received 37 millimeters of rain in one hour. Earlier, between about 5 and 6 a.m., Mokpo was hit by torrential rain of up to 65 millimeters per hour, leading to an emergency disaster alert for heavy rain.

Since Saturday, as much as 243 millimeters of rain has fallen on Mount Halla on Jeju Island. More than 100 millimeters of rain was concentrated along coastal areas of South Jeolla and Gwangju, including 132.8 millimeters in Samho, Yeongam County, 131.5 millimeters in Suyu, Jindo County, 128.1 millimeters in Mokpo and 116.5 millimeters in Solaseado, Haenam County. Heavy rain advisories and warnings were issued for parts of South Jeolla and Gwangju, South Gyeongsang and Jeju.

The Ministry of the Interior and Safety raised its heavy rain crisis alert from "attention" to "caution." Eleven cases of damage, including flooded roads and fallen roadside trees, have been reported as of the morning, but no casualties have been confirmed. Authorities also restricted access to 91 sections of Mount Jiri, Mount Wolchul, Dadohae and Mount Halla national parks and 162 other locations, including riverside walking trails and bridges.

South Gyeongsang received less rain overnight than initially feared, but the risk has not passed. Rainfall of 30 to 50 millimeters per hour is possible along the western southern coast of South Gyeongsang and near Mount Jiri through Sunday afternoon, with more than 70 millimeters per hour possible in some areas. Another round of torrential rain of 30 to 50 millimeters per hour is forecast early Monday, particularly along the western southern coast of South Gyeongsang and the central southern coast of Busan and South Gyeongsang.

From Sunday through Monday, rainfall of 100 to 200 millimeters is forecast along the western southern coast of South Gyeongsang and near Mount Jiri, with more than 250 millimeters possible in some areas. Busan, Ulsan, the central southern coast of South Gyeongsang and inland areas of South Gyeongsang are expected to receive 50 to 150 millimeters, with more than 200 millimeters possible in Busan and along the central southern coast of South Gyeongsang.

South Jeolla and Gwangju are forecast to receive 50 to 100 millimeters, with more than 200 millimeters expected along the eastern southern coast and more than 150 millimeters along the western southern coast and near Mount Jiri.

The torrential rain was caused by a low-pressure system moving northeast over the Yellow Sea interacting with a low-level jet, a strong southerly wind in the lower atmosphere. Hot, humid air carried by the low-level jet is being forced sharply upward as it encounters the terrain along the southern coast and Mount Jiri, creating rain clouds over narrow areas that can lead to large differences in rainfall even within the same city or county.

Heavy rain falling over a short period in areas dried out by drought increases the risk of soil runoff and landslides. Torrential rain can rapidly flow over the ground, potentially causing rivers to overflow, soil to wash away, retaining walls to collapse and landslides. People near valleys or rivers should immediately move to a safe location once rain begins.

Strong winds are another concern. Gusts exceeding 20 meters per second (45 miles per hour) are forecast in some areas along the southern coast. Waves of up to 3.5 meters (11.5 feet) are expected in offshore waters of the South Sea and East Sea. Sea levels are also particularly high through Sunday, raising the risk of flooding in low-lying areas along the southern coast or sewage backing up around high tide.

Rain is expected to continue across most of the country through Monday morning and on Jeju Island through Monday evening. Seoul and other parts of central Korea are generally forecast to receive 20 to 60 millimeters from Sunday through Monday, with the rain easing temporarily in many areas Sunday afternoon.

Atmospheric instability, however, could bring showers of 5 to 60 millimeters across the country from Monday afternoon into the evening. Rain is also forecast for the Gyeongsang region and Jeju on Tuesday, with showers expected in parts of southern Korea in the afternoon.

Hot weather will return after the rain ends. Daytime highs will remain between 24 and 30 degrees Celsius (75 to 86 degrees Fahrenheit) on Sunday because of the rain and wind, before rising to between 27 and 32 degrees Celsius on Monday and 29 to 33 degrees Celsius from Tuesday.

From Thursday through Aug. 26, daytime temperatures are expected to reach 29 to 34 degrees Celsius, higher than the seasonal average. The KMA forecasts apparent temperatures of around 33 degrees Celsius across most of the country, with tropical nights expected in many areas.

BY RHEE ESTHER [yoon.soyeon@joongang.co.kr]