Heavy Rains And Heat Wave Grip South Korea

As South Korea steps into mid-September, the nation is bracing for a dramatic shift in weather, with heavy rainfall and sweltering heat set to collide across its regions. According to multiple meteorological reports, from the late hours of September 16 through September 17, 2025, nearly every corner of the country will experience a bout of rain—sometimes intense—alongside persistent high temperatures, particularly in the southern regions and Jeju Island. It’s a forecast that has officials urging residents and travelers alike to stay alert and prepared.

The central and northern regions are expecting the skies to open up late on the 16th, with rain spreading across most areas by the following morning. The Korea Meteorological Administration has predicted that the central and northern parts of the country, including Seoul, Incheon, Suwon, and Chuncheon, will see rainfall amounts ranging from 20 to 60 millimeters, with some localized downpours possibly exceeding 80 millimeters. The rainfall isn’t expected to be a gentle drizzle either—sudden, powerful showers could bring as much as 30 millimeters of rain per hour, especially in regions like Chungbuk, according to Jungbu Maeil.

Residents in Chungbuk are being told to keep an eye on the sky, as the region is forecasted to receive between 5 and 40 millimeters of rain. The showers will hit sporadically through the morning and evening of September 16 before intensifying overnight and continuing into the next day. The local authorities have warned that, in places where the rain falls hardest, flash flooding in valleys and rivers is a real risk. "With short bursts of heavy rainfall, water levels in valleys and streams can rise suddenly. Please avoid approaching or camping near these areas, and if the sky suddenly darkens, move to a safe place," a meteorological official told Jejusori.

Jeju Island, often a bellwether for the nation’s weather extremes, is also preparing for a deluge. From the morning of September 16 through late afternoon, the island is expected to see 5 to 40 millimeters of rain, with some spots possibly soaking up more than 60 millimeters. The rain isn’t coming alone—thunderstorms and gusty winds are expected to sweep through, adding to the hazards for those living on or visiting the island. The weather service has already issued a heat wave advisory for coastal areas, warning that the combination of high humidity and temperatures will make conditions particularly uncomfortable.

“Currently, a heat wave advisory is in effect for coastal regions, and the weather will remain humid with high perceived temperatures,” noted the Jeju Meteorological Administration, as reported by Jejusori. Temperatures on Jeju are forecasted to start at a balmy 25 to 27 degrees Celsius in the morning and climb to 31 to 33 degrees by afternoon on September 16. The following day, the pattern holds, with morning lows at 25 to 27 degrees and highs of 30 to 32 degrees. These figures are notably above seasonal averages, making the rain’s arrival something of a mixed blessing—offering brief relief from the heat, but also bringing the risk of sudden storms and flooding.

Elsewhere across the peninsula, similar patterns are expected. According to Jeonmae Ilbo, the southern coastal cities—Busan, Ulsan, and Gyeongnam—will see rain amounts between 5 and 20 millimeters, while the central-northern eastern coast, Chungcheong, and Jeonbuk regions are forecasted to get 10 to 40 millimeters. The weather will be at its hottest in the southern regions, with temperatures peaking at 33 degrees Celsius. The heat, paired with the moisture-laden air, will make for muggy and potentially uncomfortable days, especially for those living or working outdoors.

The daily temperature swings are expected to be less dramatic than usual, with overnight lows remaining high. On September 16, morning temperatures nationwide are predicted to range from 19 to 25 degrees Celsius, with afternoon highs climbing to between 28 and 33 degrees. The following day, September 17, will see slightly cooler conditions, with morning lows at 22 to 25 degrees and highs between 26 and 28 degrees in the central regions. While the heat is expected to persist in the south, the north and center of the country may start to feel a bit of relief as the week progresses.

Despite the impending rain, air quality is expected to remain generally good, with fine dust concentrations across the country forecasted to stay at “good” to “moderate” levels, thanks to efficient atmospheric circulation. At sea, the waves are predicted to be moderate, with heights of 0.5 to 1.0 meters along the coasts and up to 2.0 meters in the open waters of the West Sea, according to Jeonmae Ilbo.

For many, these weather warnings come as a timely reminder of South Korea’s late summer volatility. The combination of lingering heat and sudden rains is a hallmark of the season, often catching residents off guard. Authorities are urging the public not to underestimate the risks, especially in areas prone to flash flooding or landslides. “When showers or rain fall, gusty winds or lightning may occur, so be prepared for various accidents,” Jeonmae Ilbo cautioned in its forecast, emphasizing the importance of vigilance during these unpredictable weather events.

For those hoping to enjoy the outdoors—perhaps a stroll through a buckwheat flower field in Cheongju or a trip to Jeju’s famed beaches—timing will be everything. The advice from meteorologists is clear: if the skies darken suddenly, seek shelter immediately, and avoid camping or hiking near rivers and streams until the rain subsides. With the ground already saturated in some areas, even a brief thunderstorm could trigger rapid rises in water levels.

Interestingly, while the rain is expected to bring some respite from the oppressive heat in the central and northern regions, the south may continue to swelter. The phenomenon of “tropical nights”—when overnight temperatures remain above 25 degrees Celsius—is likely to persist along the southern coast, making for restless nights and increased health risks for vulnerable populations.

In the end, this week’s weather is a vivid reminder of the dynamic and sometimes dramatic climate that defines South Korea’s late summer. From pounding rain and rolling thunder to relentless heat and humidity, residents are being asked to stay alert, plan ahead, and look out for one another as the nation rides out this latest meteorological rollercoaster.