It's the combination of heat and humidity that's deadly. The desert is hot but dry so you can rely on evaporative cooling but if it's too wet then there is nothing you can do to cool your body.
Having experienced the few last summers at 80% humidity and 32oC+, i can say from my experience that the extreme is becoming the norm now. In fact i am enjoying it right now, and it has just rained half an hour ago!