The real temperature are 58ºC, but relevant is the index, that is, how we percive the temperature. With a dry air you can support more than 70º (eg in a Sauna), but with high air humidity, which evite the evaporation cooling by your sweat, even 50ºC result lethal in a short time, rising corporal temperature over 43ºC. Because of this, it's the index which is the relevant value, not the one shown by the thermometer.
With a dry air you can support more than 70º (eg in a Sauna), but with high air humidity, which evite the evaporation cooling by your sweat
You got that flipped.
With dry air, your sweat can evaporate. Evaporation consumes energy, and thus has a cooling effect, making high temperatures more bearable/survivable at low humidity.
With humid air (eg in a sauna) your sweat cannot evaporate because the air is already saturated. This deprives you of the cooling effect, making humid conditions feel much hotter; and making it lethal much faster and at lower temps.
I see the confusion. A sauna is not necessarily humid, traditional Finnish sauna are hot but not high humidity. You're thinking of a steam sauna which is high humidity but lower temperature.
100f+ degree weather with zero humidity? Sweat evaporates so quickly that with a fan on you or a breeze you can actually feel briefly chilled at times.
But mentioning the actual temperature is less misleading.
With a dry air you can support more than 70º (eg in a Sauna), but with high air humidity, which evite the evaporation cooling by your sweat, even 50ºC result lethal in a short time,
Over 90C dry, 50C wet, 10-15 minutes. Longer/hotter if you take dips in cold water to cool down or if you're Finnish. They sometimes go over 100C, they're used to it.
Is hot but Washington Post article says the temperature in recent weeks has got as high as 51C and all time max is 54C. Where are you getting 58C from?