Clear skies and typhoons that veered away from the Korean Peninsula left September as the second-driest on record nationwide. Temperatures ran above the long-term average, though the month was cooler than the record autumn heat of the past three years.
Nationwide rainfall last month totaled 26.4 millimeters, according to the Korea Meteorological Administration's September climate report released on the 3rd. That was 17.0% of the long-term average of 155.1 millimeters, the second-lowest figure on record. It was about one-ninth of the 228.8 millimeters recorded in September last year. The number of rainy days came to 4.4, less than half the average of 9.3 days.
Migratory high-pressure systems settled over the country, bringing extended periods of clear weather, while cold, dry air flowed in from the north, holding rainfall to unusually low levels. With little rain, relative humidity averaged 73% last month, the fifth-lowest on record.
The absence of typhoons moving north also contributed to the low rainfall. A total of 26 typhoons formed in the northwestern Pacific through September this year, but only one — Typhoon Jangmi, the sixth of the season, which formed in May — affected Korea. The pattern has repeated over the past three years, with one typhoon affecting Korea in 2023, two in 2024 and none last year.
The weather agency found little correlation between Korea's exposure to typhoons and either the total number of storms or where they formed. The North Pacific high, however, has recently expanded farther northwest than usual, creating conditions that make it difficult for typhoons to reach the country. The farther northwest the high-pressure system extends, the more likely typhoons are to track toward China or Taiwan. Upper-level troughs that would otherwise steer storms toward Korea were also blocked by the high.
Temperatures exceeded the long-term average. The nationwide average temperature last month was 21.7 degrees Celsius, 1.2 degrees above the average of 20.5 degrees. It marked the sixth consecutive year in the 2020s with a warmer-than-average September. The North Pacific high, which expanded in late August, lingered into early September and pushed temperatures higher. Highs climbed sharply from the 21st to the 24th in particular, producing abnormally hot conditions across most of the country.
Still, the month was cooler than 2023 through 2025, which rank as the three warmest Septembers on record. Cold air moved down from the north this year, and the North Pacific high retreated to the southeast relatively quickly. Convective activity in the tropical western Pacific was also weaker than average, which sapped the strength of the high.
"This year saw sharp temperature swings as cold air flowed in from the middle of the first third of September, and rainfall was unusually sparse," said Lee Mi-sun, administrator of the Korea Meteorological Administration. "Climate variability has been increasing lately, and we will do our utmost to strengthen advance preparations for abnormal weather."
