October Average Temperature Rode a "Roller Coaster" as Daytime Highs Unusually Hit 30 C

Daily average temperature fell 10 degrees in three days
El Niño brought warm, humid air from the south

With temperatures riding a roller coaster, the national average temperature last month was the fifth-highest on record.

Yonhap News Agency

According to the Korea Meteorological Administration's climate analysis on Nov. 4, the national average temperature last month was 15.8 degrees Celsius, 1.5 degrees higher than the October average of 14.3 degrees Celsius for the 1991-2020 climate normal. The average temperature last October ranked fifth-highest among the 54 Octobers from 1973 through this year, the year nationwide weather observation coverage was expanded and became the benchmark for various weather records.

From Oct. 10 to 13 and from Oct. 16 to 20, high-pressure circulation developed over the country as warm air flowed in from the south, causing temperatures to rise unusually sharply. On Oct. 12, Seoul's daily high reached 30.1 degrees Celsius, breaking the record for the highest October temperature since observations began. These unusually high temperatures drove up the monthly average.

Another notable feature was the roller-coaster-like fluctuation in temperatures last month. This was due to the continued smooth west-to-east flow of air high above the mid-latitudes, which brought cold and warm air into the country in alternation. The national daily average temperature fell 10.0 degrees from 19.8 degrees on Oct. 18 to 9.8 degrees on Oct. 22. Three days later, on Oct. 25, it rose 7.1 degrees to 16.9 degrees, before falling another 8.8 degrees to 8.1 degrees on Oct. 28.

In the second half of last month, warm, humid air flowed in from the south, while a strong blocking pattern developed near the Ural Mountains, disrupting atmospheric flow. Cold air from the north frequently moved into the country, causing sharp temperature fluctuations and heavy rainfall. As during the monsoon season, air masses with different characteristics collided, forming bands of rain clouds.

El Niño was behind the increase in precipitation. As El Niño developed, convective activity over the tropical western Pacific declined compared with normal years, leading to the development of high-pressure circulation over the Philippine Sea. As energy propagated through the atmosphere, atmospheric waves formed, bringing alternating areas of high and low pressure. This led to the development of high-pressure circulation southeast of Korea, along the edge of which warm, humid air flowed in from the south.

As a result, precipitation last month totaled 108.5 mm, 1.7 times the October average of 63.0 mm. Rainfall was light during the first third of the month but heavy in the middle and latter thirds, increasing the overall total. Despite the heavy rainfall, the number of days with meteorological drought was the fourth-highest on record, at 18.5 days. Meteorological drought refers to a situation in which the Standardized Precipitation Index, based on cumulative precipitation over six months, falls below a certain level. This is why the number of drought days was high despite the heavy rain last month.

Meanwhile, the average sea surface temperature in waters around Korea last month was 22.7 degrees Celsius, the third-highest in the past 10 years (2017-2026), after 23.5 degrees in 2025 and 23.3 degrees in 2024. This was 0.9 degrees higher than the average for the past 10 years.

This content was produced with the assistance of AI translation services.