Who said September means autumn? Erratic weather swings from last year's heat wave to this year's drought

Nationwide rainfall last month fell to just 17 percent of the historical average, the second-lowest September total on record, as South Korea's climate continues to swing between extremes from one year to the next. Unlike recent years, when record heat stretched well into September, this year saw temperatures drop to near-normal levels in the middle of the month while rainfall remained unusually scarce — a pattern that underscores growing climate volatility.

According to the Korea Meteorological Administration's "September 2026 Climate Characteristics" report released Friday, nationwide precipitation last month totaled 26.4 mm, or 17.0 percent of the historical average of 155.1 mm. The figure is the second-lowest for September since records began, trailing only 1982, when rainfall reached 20.6 mm. Compared with last September's 228.8 mm, this year's total was roughly one-ninth the level.

The number of rainy days also fell sharply, averaging 4.4 days against the historical norm of 9.3 days — a shortfall of 4.9 days. Rainfall during the middle 10 days of September was particularly sparse, reaching just 0.7 mm, the lowest mid-September figure on record. Some rain did fall in early September due to a stationary front and again in late September from a low-pressure system, but amounts were minimal. The KMA attributed the dry conditions to a dominant upper-level anticyclonic circulation, the influence of migratory high-pressure systems that kept skies clear, and an influx of cold, dry air from the north.

The prolonged dry spell triggered meteorological drought conditions across the country. The nationwide average number of drought days last month reached 12.8, the sixth-highest on record. By region, North Jeolla Province recorded the most drought days at 19.2, followed by South Gyeongsang Province (18.5 days), the Greater Seoul metropolitan area (16.5 days), North Gyeongsang Province (14.4 days), and South Jeolla Province and Gwangju (14.3 days). Cumulative nationwide rainfall from April through September this year was limited to 72.7 percent of the historical average.

Temperatures last month remained above the historical average. The nationwide mean temperature for September came in at 21.7 degrees Celsius, 1.2 degrees above the norm of 20.5 degrees. Since 1973, the country's average September temperature has risen at a rate of 0.39 degrees per decade. Since the 2020s began, September temperatures have exceeded the historical average for six consecutive years.

However, the magnitude of this year's warming was relatively modest compared with the record heat of the past three years. The hottest September on record remains 2024, when the average reached 24.7 degrees, followed by 2025 at 23.0 degrees and 2023 at 22.6 degrees.

In contrast, cold air from the north pushed in from Sept. 5 through mid-month this year, and the North Pacific high-pressure system retreated rapidly to the southeast, keeping temperatures near normal during that period. As a result, this September's average temperature ran 0.9 to 3.0 degrees below the figures recorded over the past three years.

Temperatures rebounded at the start and end of the month. The North Pacific high that had influenced South Korea since late August brought heat waves and tropical nights to parts of the southern regions and Jeju in early September. Temperatures rose again in late September as upper-level anticyclonic circulation strengthened. An unusual warm spell spread across most of the country from Sept. 21 to Sept. 24. The nationwide average daily high in late September reached 26.6 degrees, the highest on record for that period.

The KMA cited an influx of cold air from the north and weakened convective activity over the tropical western Pacific as the main reasons September this year was not as hot as the previous three years. In those years, vigorous convection near the tropical western Pacific and the Philippine Sea had driven the North Pacific high to expand northwestward, funneling hot, humid air into the Korean Peninsula. This year, convective activity was suppressed below normal, limiting the high's expansion.

"Climate volatility has been increasing in recent years, with different climate characteristics emerging each year," Korea Meteorological Administration Commissioner Lee Mi-seon said. "We will closely monitor current climate conditions and strengthen our preparedness against abnormal weather events."