Rain will fall nationwide except on Jeju from Monday, July 20, through Tuesday, July 21, under the influence of a stationary front, Kyunghyang Shinmun reported, citing the Korea Meteorological Administration. More rain is expected later in the week, leaving virtually the whole week wet.

A stationary front is the boundary where two air masses of different character collide. It drifts north and south, dumping rain concentrated in a narrow band. On the same day, rainfall directly under the front and a little distance away can differ several-fold.

Why forecasting is hard

A shift of a few dozen kilometers changes which city floods. The weather agency therefore updates hourly rainfall by region at short intervals and urges residents not to check the forecast once and be done.

Over the weekend, flood alerts were issued for Seoul's Gangseo, Eunpyeong and Mapo districts, a heavy-rain warning for Pocheon in Gyeonggi, and advisories for six areas including Namyangju—the classic monsoon pattern of intense rain over a small area in a short time.

Practical preparation

Semi-basement and low-lying homes and underground garages face the greatest risk. Clear objects off drains, and avoid parking along streams. Once water enters an underground space, evacuation comes first; every year people are hurt trying to save vehicles or property.

For Chinese-heritage families and students in Korea, language is an added risk. Emergency alerts from the weather agency and the interior ministry arrive in Korean, but a growing number of municipal foreign-resident support centers and Chinese associations issue parallel Chinese guidance. Checking your district's contact point in advance helps.