The sources I looked at (e.g. [0]) suggest a maximum temperature of 91 F with a humidity of maybe 72 %, equating to a wet bulb of 28.51 C [1].

Are you sure about those temperatures/humidities? 100 F with 99 % humidity equates to a wet bulb of 37.75 C [2], well above the commonly accepted theoretically survivable limit of 35 C.

[0] https://www.weatherwx.com/hazardoutlook/sc/fort+jackson.html

[1] https://www.omnicalculator.com/physics/wet-bulb?advanced=1&c...

[2] https://www.omnicalculator.com/physics/wet-bulb?advanced=1&c...

I remember specifically days where we woke up and it was already 96 degrees and there were still puddles from the rain the previous day.

I think what it means to survive those temperatures may be the issue here, because obviously you don't just drop dead if you are a healthy 18 year old. An obese 65 year old will be long dead in an environment that a healthy 18 year old can run wind sprints in.

100F + 100%RH == ~195F Heat Index. That is WELL into the Black Flag range. Under a black flag, even the military does restricted work periods if they must be out.

> A black flag weather condition is in effect when the temperature reaches 90 degrees or higher, according to the Safety Office's heat stress card. In this category, only 10 minutes out of each hour should be spent engaging in strenuous activities, only 20 minutes should be spent performing moderate work and 50 minutes could be spent doing easy work. Strenuous work includes intense jogging and walking on hard surfaces at 3.5 mph with loads of 40 pounds or more. Moderate work includes performing calisthenics and easy work includes marksmanship training and light walking with no load. Community members should drink one quart of water per hour while performing any type of work while a black flag is raised.

Please go back to 1999 and tell my drill sgts about this.

This was my reaction, too. Anecdotally, I used to bike in a hot and humid environment. My first century ride (100+ miles in one sitting) was on a day that hit above 100 degrees with at least 80% humidity. I was able to train like that, 3-6 hours in the sun, more or less every day of the summer in similar conditions.