Is Autumn Truly Here? The Persistent Heat and Humidity Ahead

As summer heat waves and heavy rains subside, many might expect the cool breezes of autumn to settle in.

As summer heat waves and heavy rains subside, many might expect the cool breezes of autumn to settle in. However, despite some cooler temperatures in recent days, warmer and more humid conditions are expected to return starting from September 25th. This blog explores the reasons behind the fluctuating weather and why, meteorologically speaking, summer isn’t over just yet.

After torrential rains hit southern Korea on September 21st, cool air from the north brought a temporary respite in the form of cooler temperatures. According to the Korea Meteorological Administration (KMA), this sudden change is due to cold, dry air replacing the warm, humid air that had been dominant. The cold air, driven by a low-pressure system, is responsible for the cooler temperatures, but this relief will be short-lived. From September 25th onward, hot and humid conditions are expected to return periodically until mid-October.

This weather shift is linked to the weakening of the Tibetan High, which has allowed colder northern jet streams to push into the Korean Peninsula. As a result, a monsoon front developed, pulling in tropical low-pressure systems that caused the heavy rains in the southern regions. However, the cold air descending from the upper atmosphere will not stay for long, as warmer winds from the south are expected to bring back the high temperatures.

Kim Hae-dong, a professor of Earth Environmental Studies at Kyungpook National University, explained that the persistent heat is due to the North Pacific High, which normally weakens by late August, holding strong until mid-October this year. He emphasized that while it may feel cooler occasionally, the average daily temperature needs to consistently fall below 20°C to be considered autumn by meteorological standards. With daytime temperatures still hovering around 24–25°C, it’s safe to say that, for now, we are still in a ‘meteorological summer.’

Though the cooler weather brings brief relief, autumn isn’t quite here yet. With fluctuating temperatures and persistent humidity, we can expect a continuation of summer-like conditions for a few more weeks. As the North Pacific High gradually weakens, we’ll likely experience more definitive autumn weather—but not just yet. Until then, it’s important to be prepared for the ongoing temperature swings and occasional heat spikes.