מזג האוויר בסיאול במאי

May in Seoul is the month that changes under you: regulars say the first week still wants a light jacket or a cardigan, and by the last week you rarely need more than a t-shirt. Their figures - highs of 20 to 25C, lows of 13 to 16C - bracket our row's 24.2C and 13.7C. The standing advice is layers, because the drop in the early morning and again in the evening is the part visitors get wrong, and the jacket they recommend is one that will also shed rain. That last point is the one our row sharpens: 105.2mm falls in May across 8.1 days, more than the spring reputation suggests, and it arrives well before the proper summer monsoon. The record: humidity 71 percent, 10 hours of sun and AQI 86.

Regulars describe typhoon risk this month as genuinely random rather than a serious, consistent threat - even when a significant one is forecast, the actual disruption typically runs two to three days rather than derailing a whole trip, and August is named as the more typhoon-prone month by comparison. Our row backs a still-warm, humid read, 27.5C reading as a hot 30C at 79 percent humidity, over 18.7C nights, with a real 148.2mm of rain across 9.1 days. Regulars call the back half of the month into early October one of the best overall windows of the year, pleasant and not too hot. Summer clothes plus a light jacket for cooler evenings or rural areas is the standard advice. The sea sits at 25.8C. The record: 8.2 hours of sun, a 12.6 kph wind and AQI 73.

August is the hottest month here and regulars measure it in minutes: ten outside and you are sweating. Our row gives 31.2C reading as 36C at 83 percent humidity over 24.2C nights. The jangma has usually finished by the end of July, so this is not everyday rain - but it is the wettest month we hold for the city at 243.6mm across 14.5 days, which means it arrives hard when it comes. Typhoon season overlaps and nobody can schedule one; the board's wry consolation is that a typhoon at least breaks the heat for a day or two. Anything outdoors belongs to early morning or after dark. The record: 8.6 hours of sun, a 28.4C sea and AQI 93.

June here is two months in one and regulars date the join: the first half is hot by day, cooler at night and mostly dry, and around the fourth week the jangma arrives and turns it wet and sticky. Our 115.7mm across 8.9 days is that shape, not an evenly damp month - most of it falls in the last week or so. Before then the numbers are kind: 28.5C reading as 30C at 75 percent humidity, nights at 19.4C, and 14.7 hours of daylight. Anyone with a choice inside the month should take the first fortnight; anyone arriving late should expect heavy showers rather than all-day rain. The record: 10 hours of sun, a 22.6C sea and AQI 86.

Seoul forum threads describe January as the coldest month of the year, typically ranging from about -6C to 3C but with posters warning that cold Siberian winds can push it down toward -20C on the harshest days, and that it can feel bitterly cold even under clear sun. Snow is a real possibility through the month, though whether a given trip sees actual snowfall was described as largely down to luck. The consistent advice across threads was serious winter gear - a proper coat, thick scarf, gloves and warm footwear - after which posters were clear that sightseeing stays fully doable, helped along by Seoul's extensive indoor museums and shopping options for the coldest stretches.