Source: Chosun Biz

What happened

On Oct. 12, 2026, Seoul’s daytime high reached 30.1 C, the highest October reading since modern observations began in 1907, Chosun Biz reported from the Korea Meteorological Administration. The previous October mark was also 30.1 C, on Oct. 3, 1913. The numbers match; the ranking flipped because when two records are identical, the more recent date is listed first.

Daejeon hit 31.5 C, 0.3 C above its prior October high of 31.2 C set Oct. 3, 2021 (observations there since 1969). Other October records fell in Jeongeup (31.1 C), Cheongju (30.6 C), Gumi (30.0 C), Sangju (29.5 C), Andong (29.0 C), Yeongwol (29.8 C), Wonju (29.3 C), Chuncheon and Jeongseon (28.8 C), and Icheon (29.1 C).

A News1 photo the desk ran from Myeong-dong showed foreign visitors in light clothes walking past a store already hanging winter padded jackets — the visual of a mid-October heat spike colliding with a retail calendar that had already moved on.

The breakdown

The KMA’s analysis, as relayed by Chosun Biz: hot, humid southerly winds were funneled between a high to the southeast of the peninsula and a trough to the southwest. That is a late-season setup, not a summer typhoon leftover.

The same piece then pivots to the exit ramp. Rain was forecast nationwide from the night of the 12th through daytime on the 13th, after which northern cold air would drop Oct. 14 morning lows to 5–14 C. Oct. 13 mornings stay mild (15–20 C vs. average 7–16 C); daytime highs 20–26 C sit near average. City pairings for the 13th: Seoul / Incheon / Daejeon 17 C / 22 C; Gwangju / Ulsan 18 C / 24 C; Daegu 17 C / 24 C; Busan 20 C / 24 C.

Rain amounts in the forecast: Jeju 10–60 mm (over 80 mm in some mountains); capital area, inland/mountain Gangwon, and Chungcheong 10–50 mm; Gwangju / South Jeolla 5–50 mm; North Jeolla, Busan, Ulsan, South Gyeongsang, Daegu, North Gyeongsang, Ulleungdo, and Dokdo 5–40 mm; West Sea islands and the Gangwon east coast 5–30 mm. From the night of the 13th, gusts around 55 km/h (70 km/h in mountains). Offshore, central West Sea winds 30–60 km/h and waves 1.5–3.5 m, then rough water spreading on the 14th.

Why it matters outside Korea

If you packed for “nice October in Seoul,” you packed for a brochure, not this week. The operational fact is a same-week swing: a 30 C city day, then rain, then single-digit mornings. That hits Incheon arrivals, palace outdoor days, school trips, and anyone who shipped a winter wardrobe to a locker they cannot open until Thursday.

It also changes how you read Korean October coverage. A 119-year ranking is a headline. The traveler’s number is the 14th’s 5–14 C morning band and the ~15 C day-night gap that shows up again later in the month when frost hits Gangwon.

What travelers and expats should watch

• Do pack a layer you can add after the rain, not only a T-shirt for Myeong-dong photos. Oct. 14 mornings in the KMA band will feel like a different season than the 12th.
• Don’t lock an outdoor shoot or a Han River picnic for the 13th on the 12th’s sky. Rain starts late on the 12th in the capital area and can linger into the afternoon in parts of South Gyeongsang.
• Expect ferry and small-craft disruption if you had a West Sea or Jeju water day: the desk’s wave and wind numbers are the watch, not a generic “typhoon rumor.”
• Re-check pharmacy and convenience-store hours if you are heat-sensitive; a 30 C October afternoon in dense shopping streets is still a heat-health day even when padded jackets are on the rack.

Context

Read this as a two-step weather week — record heat, then a hard cool-down — not as proof that “Korea’s October is now summer.” One tied century-scale high does not rewrite the whole month. It does mean you should stop dressing from the souvenir calendar and start dressing from the KMA’s next 48 hours.

Source

Primary: Chosun Biz, Oct. 12, 2026 (English; KMA figures and city records as reported). Korelay paraphrase for overseas packing and itinerary timing; not a substitute for the live KMA forecast.