>>1429385Anon, please read about wet-bulb temperature and heat stress index.
Yes, there's a big difference between wet heat and dry heat. In very simple terms high humidity requires you wear as little or as light of clothing as possible (i.e. as is appropriate to the air temp and humidity) while dry hear requires you protect yourself from the sun and stay hydrated as you'll dehydrate faster. In extremes one isn't necessarily more deadly than the other, but in practice high humidity tends to be more deadly as your body's natural thermoregulation systems rely entirely on evaporative cooling which is inhibited or completely negated in high heat/humidity conditions.
Staying hydrated is essential in any hot condition but you're more likely to have unexpected heat exhaustion or heatstroke in humidity.
Anecdote: I took my mountain bike out on a 95% humidity day when it was about 87ºF/30ºC and almost died (had full on disorientation: tunnel vision, confusion, stumbling, nausea, etc). I dumped my cool drinking water on my back and it brought me right back from the brink. I honestly became so overheated, blind, and panicked that I would have rolled in mud if there was any nearby without a second thought.
That's when I did my research and figured out there's a lot more going on than just temperature. You have to be mindful of the conditions.
