We have all heard the old saying “it’s not the heat, it’s the humidity”, you may have even said that these past few days, but what you really should be saying is “it’s not the heat, but the dew point”. Relative Humidity is exactly that, relative and is directly correlated to the air temperature.
Instead, you feel uncomfortable base on the amount of water vapor in the air, which is not what relative humidity is measuring. The past few days the relative humidity has dropped to around 50-60% during the afternoon when the heat indexes were at the highest point of the day.
A better way to know what your comfort level will be is to watch the dew point and remember that dew points in the 40s you’ll be feeling great, in the 50s, you’re still comfortable, moving through the 60s, most feel slightly uncomfortable, but when the dew points are in the 70s (the case the past few days) no matter what the temperature, nearly everyone is uncomfortable and the word sultry will probably come to mind.