For weather-sensitive travel, use Korea Meteorological Administration (KMA) as the official forecast and warning source. Its English site provides current weather, forecasts and severe-weather alerts for land and sea.
The alert categories include heatwave, heavy rain, heavy snow, typhoon, strong wind, wind wave, surge, cold wave, dryness, Asian dust, fog and tsunami. A warning can apply only to a specific county, mountain zone or sea area, so match the alert location to the exact place you plan to visit.
This matters most for hiking, ferries, islands, beaches, coastal walks and mountain roads. A normal city forecast does not prove that a sea route or high-elevation trail is safe. Check both the general forecast and the severe-weather alert page before departure.
For public-safety instructions and local emergency messages, pair KMA with Safe Korea/Emergency Ready. KMA tells you the meteorological warning; Safe Korea can surface local government emergency alerts and nearby safety facilities.
Forecasts change. Recheck on the morning of travel and again before boarding a ferry or starting a long hike when warnings are active or expected.