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Comment by gavmor | Hacker News Reader

44C can be fatal at even 10% humidity[0]. Hanoi never sees humidity below 78% (in January[1]), so unless I am confused about Wet Bulb Temperatures, anything above 30C will see otherwise healthy individuals drop dead in the street after six hours outside[2]. 44C is utterly horrifying to contemplate.

0. https://arielschecklist.com/wp-content/uploads/2017/01/CHART...

1. https://www.climatestotravel.com/climate/vietnam/hanoi

2. https://research.noaa.gov/article/ArtMID/587/ArticleID/2621/...

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I googled for "wet bulb calculator" and it lists 44C 10% humidity as 21C wet-bulb, which is certainly not deadly for healthy people with access to water and shade. 78% relative humidity though is 40C which is unfathomably hot.

I should point out that relative humidity usually goes down when temperatures go up (because the absolute humidity rises rather slowly), so hopefully it was lower than 78% humidity.

[edit]

Chart from parent post is not WBT but WBGT. See e.g. https://axongroup.com/en/blog/what-wet-bulb-temperature for an actual wet-bulb temperature chart.

I’m not sure I understand the chart in [0]. Isn’t wet bulb temperature supposed to be the same as air temperature when relative humidity hits 100%? If so, why does that chart show wet bulb temperatures above air temperature at humidities above 50%?

I'm sorry, that chart indicates Wet Bulb Globe Temperature, which also accounts for "solar load" or, per wikipedia[0] "solar radiation," ie the heat of the sun bearing down, as well.

0. https://en.wikipedia.org/wiki/Wet-bulb_globe_temperaturealc

Keep in mind, RH drops as temperature rises. Experienced the same in Florida. Every once in a while you'd get a super hot day, but the humidity would read lower than usual.

The humidity at 44C was probably in the 40s.

Not that any of this is good news, just trying to clarify it wasn't 44C at 78% RH. That would be insanely deadly.

I don’t know why relative humidity is used for laymen. I remember when I learned the Dew Point is what you can use to gauge what it feels like. I grew up in the South and later in life moved to the northwest and people would say it was humid sometimes in the summer and could never understand why they thought that. They’re just looking at the relative humidity on the weather app or whatever. Whatever the RH is if the dew point is 70°+ it’s gonna feel way hotter.

I came to the exact same conclusion for the exact same reasons. RH is terrible at telling you much of anything due to the nature of what it's actually measuring.

90 degrees at 60% RH is much 'muggier' than 60 degrees at 75% RH.

Agreed, dew-point is so much better than RH. Wet bulb is a good number too.

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