What could be the reason for this perceived inconsistency?

Question

The dinurnal(daily) relationship between temperature and humidity is such that the lowest humidities should occur in the afternoon hours. It is during these times, however, when it often seems to be most humid and uncomfortable. What could be the reason for this perceived inconsistency?

Answer 1

During a warm days, we will feel "humid" because of the combination of high temperatures mixed with more water vapor in the air.  When the temperature is warm, people exposed to this type of heat will sweat.  It is this sweating process that we cool off.

This sweating process is one of the main ways a human body will try to cool down.  When the humidity levels are high enough to reduce the amount of sweat being evaporated off the skin, we will feel "humid" or what most people will describe it as a sticky feeling.

One must realized that it the high temperature first that makes us feel uncomfortable.  The more the human body is exposed to the heat, the more the body will sweat to try to cool us down.  When you have more more water vapor (high RH) in the air, there will be less evaporation of water from your skin.  So you will feel "humid".  

At night, the temperature is lower, so your body does not usually need to sweat to cool down.  So the higher level of humidity at night is not much of a factor because the temperature is cooler.  To show that heat is more important factor than humidity alone, here is a question you can ask yourself.  During the winter when it is foggy and you know the humidity is at 100 percent, do you feel the humid conditions like you do during the warm season?

Answer 2

The afternoon is the time of most heat. Heat evaporates water while making the air warm so you need to consider both temperature and humidity. Hot dry air has a lot less heat than humid air several degrees cooler. Thats why deserts get so hot; temperature of dry air is a lot higher than humid air with the same heat content.