Autumn arrives a day early: temperatures to swing up to 15 degrees Tuesday

Clear skies and a wide temperature swing are forecast for Tuesday, the day before the autumnal equinox.

Autumn weather will settle across the country from Tuesday through Wednesday, according to Yonhap. The pattern is driven by a high-pressure system moving from northern China toward the northern East Sea, keeping South Korea under easterly winds through Wednesday.

Those easterly winds will dry out as they cross the Taebaek Mountains, leaving the air particularly parched west of the range — in the Chungcheong region through Tuesday and in the Greater Seoul area through Wednesday.

The temperature gap between morning and afternoon will be pronounced. Morning lows on Tuesday are expected to range from 13 to 21 degrees Celsius, while afternoon highs will reach 23 to 31 C, putting the daily swing at 10 to 15 degrees across most of the country. Some inland areas could see swings exceeding 15 degrees.

Forecast lows and highs for major cities on Tuesday are: Seoul 18 C / 29 C, Incheon 19 C / 29 C, Daejeon 17 C / 29 C, Gwangju 18 C / 31 C, Daegu 16 C / 28 C, Ulsan 19 C / 26 C and Busan 20 C / 27 C. Temperatures are expected to drop sharply overnight.

Dense fog reducing visibility to below 200 meters is forecast from the early hours through the morning on Tuesday in the inland and mountainous areas of Gangwon Province, North Chungcheong Province, and the central and northern inland areas of North Gyeongsang Province. Other inland areas can expect fog cutting visibility to under 1 kilometer. Conditions near rivers, lakes and valleys may be even thicker, and the public is urged to take care.

Swells will push into the East Sea coast, the South Gyeongsang Province coast and the Jeju coast through Wednesday. Waves may surge powerfully onto shore and at times wash over breakwaters and coastal rocks, so people should avoid approaching the shoreline unnecessarily.

Winds will also strengthen. In the southern outer waters of the East Sea, where a wind and wave advisory is in effect, winds of 30 to 60 kilometers per hour (8 to 16 meters per second) are expected through Wednesday, with wave heights of 1.5 to 3.5 meters. Seas are forecast to grow increasingly rough in the remaining outer East Sea waters, the waters off Ulsan, the eastern and western outer South Sea, and the maritime areas around Jeju.