100 degree high with 50% humidity? That's a a wet bulb temp* of 84. That leaves a good 11 degrees of safety margin before it becomes impossible for humans to survive for prolonged periods outside, even in the shade with a breeze and plenty of fluids.
*The wet bulb temperature refers to the coolest temperature a thermometer can achieve when wrapped in wet cloth and spun through the air. It is a good proxy for how well sweating works to cool the body. Once the body cannot dissipate enough heat by sweating to maintain its core temperature "... The sweating mechanism shuts down, leading to death in six hours. ... Blood vessels dilate and circulation slows, particularly to the extremities. Not enough blood will flow to the brain, affecting its functioning. You lose alertness, become drowsy, and don’t feel thirst anymore. Soon organs shut down, one by one..."
But anyway, Houston is still 13 degree of air temperature or another 35% humidity away from hitting the point where human life becomes impossible.