SEOUL - September 2025 in South Korea was the second-hottest on record, with unusually frequent rainfall and recurring thunderstorms replacing the crisp fall conditions of previous years.

According to the Korea Meteorological Administration (KMA), the average nationwide temperature in September was 23 deg C, a 2.5 degree increase from previous years.

While September 2024 still holds the record with an average temperature of 24.7 deg C, the KMA noted that this September marked the third straight year the month ranked among the top three warmest since nationwide records began in 1973.

The KMA added that the lingering influence of the North Pacific high-pressure system - which was also the main driver behind the extremely hot temperatures during the summer - contributed to driving up overall temperatures in September.

On Sept 5, Seoul logged a rare September heat wave.

Jeju Island also saw a heat wave and tropical night on Sept 25, the latest on record.

Precipitation also far exceeded norms.

On average, nationwide rainfall added up to 228.8mm, 1.5 times above the averages recorded in previous years.

The month also recorded an average total of 15 rainy days, the second-highest since weather records were first collected.

Between Sept 6 and 7, torrential rains in parts of South Chungcheong province and North Jeolla province caused severe disruptions, dumping nearly 300mm in some areas. Gunsan in North Jeolla province saw more than 100mm of hourly rainfall.

The state weather agency also reported that sea surface temperatures around the Korean Peninsula averaged 26 deg C in September, 1.5 deg C higher than the 10-year average and the second-highest in a decade.

High sea surface temperatures are often linked to stronger typhoons, raising concerns that South Korea could face severe storms later in the season.

Temperatures that are higher than the norm are expected to continue into October, as the KMA predicted to mostly see higher-than-average temperatures in that month in its one-month outlook.

The KMA stated that there is a 46.6 per cent chance that temperatures will be higher than previous years throughout October, though temperatures are expected to gradually decrease from Oct 20 onwards.

Between Oct 13 and 19, there is a 60 per cent chance for temperatures to be higher than previous years, while there is a 40 per cent chance temperatures will be higher than or similar to previous years from Oct 20 to Nov 2. THE KOREA HERALD/ASIA NEWS NETWORK