Humidity can kill you.
I live in Alabama. Normal summertime temps here are well above 90°, and in July can reach 100° or more. Relative humidity during the same time generally stays above 80%, usually above 90%.
It's like living and working in a huge sauna. And God help you if it's raining that day. With or without rain gear, you're going to be soaked within a few minutes.
I work outside in it. I have to acclimate or suffer. Often I acclimate AND suffer. One thing I've learned is that drinking constantly is a must. If you don't have to use the bathroom, you're not drinking enough. If you wait until you're thirsty, then you're already dehydrated and in danger of heat exhaustion or sun stroke. I alternate between sports drinks and straight water. I end up drinking about 3-4 quarts in a day while working, then another 1-2 when I get home and am resting. The best way to have a rough day is to not drink enough the day before.
Another thing I've learned is that a straw sombrero with a neck string is the best thing in the world. It is much cooler than any hat I've ever worn. It allows body heat to dissipate, it wicks sweat off my head and away to dry (thereby cooling me), and it provides shade. When I go indoors, or when I need to take it off for whatever reason, I can just knock it back off my head and it hangs around my neck from a string.
A third thing I've learned is that I cannot wear synthetic shirts in hot weather. I suffer. They're too constricting, too hot. They don't absorb enough moisture, and with humidity being as high as it is, they can't do an effective job of wicking it away. So I'm left squelching around in a stinky, sweaty mess. Now mind you a cotton shirt is also going to become a stinky, sweaty mess. But it takes longer for me to wet out a cotton shirt than a synthetic. Note also that I also always wear a cotton undershirt and then a cotton tee shirt on top. In fact, I wear a cotton undershirt all the time, except when sleeping. So much more comfy.
I've been reading elsewhere (ok, on Whiteblaze) where people are complaining about the high humidity in the mid-Atlantic states during the summer. I checked Google... They ain't got nothing on us. When you're used to 85-95% humidity days, then 65-75% is nothing. And the rare days when humidity drops to about 50% (it does occasionally happen) are sheer heaven -- a joy to experience. I remember in 2005 I was working on a golf course. We had a day in August where the temp was 102°, but the humidity was 47%. It was like October almost. The "realfeel" temp was something like 80°. That was the best day of the whole summer.
Those of you who hike in anything less than 80% humidity should feel very, very lucky, as should those who rarely see temps over 85°. Pray for the rest of us poor, tortured souls.
One of these days I'm going to spend some time in a place where the humidity is below 60% in the summer. It'll be next to impossible to get me to come back to Alabama.
Now, to apply this to backcountry health and safety:
I don't get to hike much in the summer, due to the nature of my job. Summer is our busy season. But I do get to go before and after the summer crunch hits, and it's almost as hot and muggy. I hike in a light-colored cotton tee shirt and a pair of thin cotton shorts. This is assuming, of course, that the temperatures are well above 70°. Anything below 75° and I start pulling out my synthetics.
I'm drinking a lot on the trail. I carry 2qts of water, not because water is scarce, but because if I don't hydrate, I will be in trouble. I try to drink both bottles by lunch, another over lunch, and then one or two in the afternoon/evening. Trust me, I sweat it out almost as soon as I drink it. It sounds like a lot of water, but some days it isn't enough.
I don't usually wear a hat while hiking in the forest. Since I'm shaded, I don't need a sunshade so much. I wear a bandanna instead, which gives me the same wicking that the straw does, and it doesn't have a brim to fight with my backpack. If I ever switch to a smaller-profile pack, I may experiment with wearing my sombrero.
Stay hydrated out there, on the trail or at home. And don't overdo it.This mean, old man died. He'd been a rather passionate Alabama fan, but he'd been so mean in life that St. Peter took one look at him and sent him off to the Devil. The Devil looked at him, asked him what he'd done to be sent to hell, and then stuck him in a cell. A day or two later, Satan came around and asked him how he was liking it.
"Oh, it's not too bad... like Memphis in June," was the reply.
"Hmph. We'll see about that!" said the Devil, and he went and turned up the thermostat. A day or two later, he went back to the old man and asked him how he liked it now.
"Well, I'm pretty happy," he said. "This is like Tuscaloosa in July."
So the old Devil thought to himself, "I'll break him!" and went and turned up the thermostat again. Again he waited a bit and then went back to the cell.
Now the man was sweating pretty bad, but his spirits were still high. When asked, he told the Devil it was like New Orleans in August.
The Devil didn't know what to do. He thought about it a bit, and then had a bright idea. He went over to the thermostat and turned it all the way down. Ice started forming across the molten lake. He went back to the cell and found the old man crying -- squalling.
"What's wrong, can't stand the cold?" the Devil asked.
The old man looked up, sniffing and sobbing.
"No. Auburn just won the national championship!"