Basically how sticky you feel. . Pay attention to the heat index. i grew up in both greater New orleans and the Oklahoma panhandle, which is semi arid. i spent year in Tucson. Arizona CAN be humid and it DOES have a monsoon season in august and September.. I am a type 1 diabetic. I've gone into insulin shock in 106 degree g weather and 6% humidity in the Oklahoma panhandle AND at in the 90s. in New Orleans, which is usually very humid. I also sun burn faster at higher elevations. I am a brunette, but pretty pale skin color but I can burn sun burn in less than half hour in Arizona., specifically meteor crater. 15 minutes and i got nice tan without T-shirt,. yes i had bra on., now i was NOT in the crater. I did master's thesis field work there in July 1982..
You feel a LOT sticker when the humidity is higher. because the sweat doesn't evaporate as fast.