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Post by chesternz on May 21, 2020 8:09:05 GMT -5
In your subjective opinion, does the heat index reflect how hot you really feel? Do you think it understates or overstates the effect of humidity? For reference: For instance, right now it's 32 C @ 70% humidity. According to the chart above, that should "feel like" 41 C. It certainly does feel hot and steamy, but probably not to that extent IMO. But personally, I just think it's trying to equate two intrinsically different things. Hot and dry heat feels completely different from (less) hot and humid heat. One time I got to experience both conditions back-to-back, which was interesting. Once I went to India in June. One day I was in Kochi with something like 33 C @ 70% humidity. The next day I was in Delhi with 40 C @ 25% humidity. I can say that the latter felt MUCH more comfortable. Both felt uncomfortably hot and made me sweat like a pig, but the difference in Delhi was that my sweat evaporated much more quickly and my shirt wasn't soaked through and sticking to my back the same way. TBH, having my clothes get soaked with sweat is much worse than the actual heat for me, so I found Delhi much better even though the heat indices would be very similar. Having said that, the heat in Delhi hit a lot harder when walking out of an air conditioned space. Somewhere like Kochi (or here in Bangkok) I notice the humidity before I notice the heat. Maybe some of you know what I'm talking about - that feeling of choking on the steamy air, like when someone forgets to open the bathroom window when taking a long, hot shower. Delhi was more like getting into your car on a hot sunny day when you forgot to crack the window.
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Post by rozenn on May 21, 2020 8:21:20 GMT -5
Yeah the HI is only useful when you don't know what a dew point is. When you know it, it doesn't serve any purpose besides bragging. A humid 33°C will feel like 33°C to a Kochi native, while a dry 40°C will feel like 40°C to a Cairo native. And both won't feel the same at all despite featuring the same cooked up HI.
Americans lol @ Canada's humidex, but the heat index is just as arbitrary. It's just geared towards a populace more used to humid heat and less used to dry heat. Doesn't make sense I know as the most populated parts of Canada get humid heat more often than dry heat, but hey those indices don't make much sense at all.
Temp + dew point is the way to go for anyone that has a genuine interest in weather.
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Post by srfoskey on May 21, 2020 12:34:32 GMT -5
I think a heat index of 110F (43.5C) feels about equally miserable regardless of humidity, so I think it works decently in terms of a measure of physical discomfort. Obviously, a temperature of 108F (42C) with a DP of 60F (15.5C) will feel different from 95F/77F (35C/25C), but both feel miserable and you feel marginally heat exhausted after walking outside for 15-20 minutes.
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Post by firebird1988 on May 21, 2020 16:37:04 GMT -5
Heat Index doesn't really tell you what it feels like, it's a measure of how effectively your body can cool itself. Similar to wind chill, which is how effectively your body can retain heat, rather than what it "feels like"
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Post by knot on May 21, 2020 16:47:44 GMT -5
It's an absolute load of bullshit. 0/10 accuracy.
Muggy air will never feel the same as its dry air equivalent.
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Post by firebird1988 on May 21, 2020 17:02:02 GMT -5
It's an absolute load of bullshit. 0/10 accuracy. Muggy air will never feel the same as its dry air equivalent. re-read my post, again it's not what it "feels like", it's how effectively your body can cool itself, and that heat index number implies how your body cools itself at that temp with a 55°F/12.8°C dewpoint. So at 90°F with a dewpoint of 78°F, your body can only cool itself as effectively as at 105°F with a 55°F dewpoint
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Post by rozenn on May 21, 2020 18:03:40 GMT -5
Indeed it is important to know how well your body can cool off in order to adjust one's activities with the outdoor conditions. That's what the T°+DP combo is for.
Why is the heat index formula different from the humidex, which is supposed to serve the same purpose? Because both have been set up empirically.
Is the 0.5*(T[°F]+61.0+((T[°F]-68.0)*1.2)+(RH*0.094)) formula any more scientifically grounded than the T[°C]+0.5555*(6.11*exp(5417.753*((1/273.16)-(1/dewpoint[K]-10)))) one? I would say no.
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Post by Ariete on May 21, 2020 18:08:16 GMT -5
The heat index is also higher for a person who is morbidly obese, drinks 8 cups of coffee, and sit in the midday sun with a black Metallica / AC/DC / Iron Maiden t-shirt and jeans, than it is for a fit well-hydrated person wearing appropriate clothing.
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Post by Morningrise on May 22, 2020 0:16:43 GMT -5
Not very accurate, IMO, it depends too much on different factors and an individual's temperature preference. And of course dry heat and humid heat feel inherently different.
And people (and weather forecasts, etc) frequently call the heat index or humidex "feels like", so I'd say judging it on that basis is perfectly reasonable. It's especially annoying when people use said index instead of the air temperature when describing the weather (e.g. "it was 40 degrees last summer!" when it never got past 33C, or whatever).
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