At 1:26 p.m. on August 2, the temperature in Yangsan, South Gyeongsang Province, rose to 42.5°C.
It is the highest figure since temperature measurements began in Korea.
That day’s forecast also included the unfamiliar term “severe heat wave warning.” When was it introduced?
3-line summary
1. The Korea Meteorological Administration’s heat wave alerts have expanded to 3 levels this year.
2. The thresholds are 33°C for an advisory, 35°C for a warning, and 38°C for a severe warning.
3. The first two require 2 days; the severe warning can be issued for just 1 day.
How was 42.5°C reached?
Yangsan’s temperature hit 42.0°C at 1:16 p.m. that day, then reached 42.5°C 10 minutes later. The day before, on August 1, the area had also reached 41.6°C.
There is a reason this figure is significant.
The Korea Meteorological Administration manages temperature rankings at 97 official observation sites nationwide. In addition, more than 550 automated temperature-measuring stations are installed across the country. The Korea Meteorological Administration said that 42.5°C is the highest record even when both groups are combined. Modern observations began in 1904, making this the highest in 122 years.
Yangsan was especially hot partly because of its terrain. In a basin surrounded by mountains, heated air has nowhere to escape and remains trapped. A high-pressure system covering the Korean Peninsula also held the heat in like a lid.
33°C, 35°C, 38°C
The criteria for heat wave alerts changed starting June 1 this year. It is the first overhaul in 18 years.
There were originally 2 levels: an advisory and a warning. One additional level has now been added above them.
| Level | Issuance criteria |
|---|---|
| Heat wave advisory | Apparent temperature of 33°C or higher for 2 or more days |
| Heat wave warning | Apparent temperature of 35°C or higher for 2 or more days |
| Severe heat wave warning | Apparent temperature of 38°C or air temperature of 39°C forecast even for just 1 day |
There is something people often miss here.
It is not the thermometer reading
33°C and 35°C are not the air temperatures shown on a thermometer; they are apparent temperatures.
Apparent temperature is calculated using both air temperature and humidity. Why is humidity included?
The human body releases heat by evaporating sweat. When the air is already full of moisture, sweat does not evaporate easily, so less heat escapes. That is why, even if the thermometer reads the same 33°C, a humid day is far more dangerous.
This is why forecasts show two figures, such as “air temperature 33°C, apparent temperature 36°C.” The alerts use the latter.
When deciding whether to go outside during the day, it is also better to use the latter.
2 days and 1 day
For the newly introduced severe warning, what matters most is not the temperature but how many days it lasts.
Advisories and warnings are issued when conditions are expected to continue for 2 or more days. A severe warning is issued even when only 1 day is forecast.
A judgment is embedded in this difference.
The 2-day requirement is based on the premise that heat becomes dangerous as it accumulates. In fact, heat-related illness patients tend to increase after hot weather continues for several days. But at around 38°C or 39°C, people can collapse in a single day. The criterion reflects the judgment that there is no time to wait for the heat to build up.
A severe warning is issued when an area already under a heat wave warning moves up one level. It is not a separate warning, but a tier above the warning.
A nighttime advisory has also been introduced
This overhaul also created a tropical-night advisory. It is issued even for just 1 day when the nighttime low is expected to be 25°C or higher.
However, this 25°C threshold is not nationwide. For large cities with populations exceeding 50만 명, as well as coastal and island areas, the threshold is 26°C; for Jeju Island, it is 27°C.
Why are the thresholds different? Cities naturally cool less at night because concrete and asphalt release the heat they absorbed during the day. The criteria separately identify when nighttime heat in those areas is unusually high.
There is also a reason nighttime matters more than daytime. The human body lowers its temperature and recovers while sleeping. If it remains hot at night, that recovery does not happen. When a heat wave continues for several days, the point at which people break down is usually not daytime, but nighttime.
The alert areas have also been divided more finely, from 183 to 235. Temperatures can differ considerably between mountainous and coastal areas even within the same city or county, but they had previously been grouped together.
Three things to check today
Look at apparent temperature, not just air temperature. If the forecast screen shows two different figures, the higher one is what your body feels.
Do not take a severe warning lightly even if it lasts only 1 day. Alerts originally required 2 days, so a warning issued for 1 day indicates that conditions are that much more intense.
Check nighttime temperatures as well. If you plan your day based only on the daytime high, you may miss the time when your body needs to recover.
You can check apparent temperature and alerts for your area on the Korea Meteorological Administration’s Weather Nuri. The detailed forecast screen displays air temperature and apparent temperature side by side, while current alerts appear on a map. To receive notifications when alerts are issued, register your place of residence in the Ministry of the Interior and Safety’s Safety Stepping Stone app.
The number to check every day is not 42.5°C
Starting this year, there are 3 heat wave alert levels, and the highest level can be issued for just 1 day. The relevant figure is not the thermometer’s air temperature, but apparent temperature, which includes humidity.
42.5°C is a record in 122 years. But that record happened once, while apparent temperature appears in today’s forecast every day.
References
- Korea Meteorological Administration press release on the heat wave alert overhaul — effective date and criteria for each level
- Korea Economic Daily report dated August 2, 2026
- MoneyToday report dated August 2, 2026
The explanation of how apparent temperature and tropical nights affect the body is based on general principles. Please consult a medical professional for decisions based on your health condition.