The sun is the major source of heat for the Earth.

Correlation between RH and Sun is -0.76

Correlation between Tmax and Sun is 0.53

Correlation between RH and Tmax is -0.41

Figure 1 ahows a very strong negative relationship between Relative Humidity and Sunshine. A moderate positive correlaion between maximum Temperature and Sunshine and a moderate negative correlation between Relative Humidity an maximum Temperature.

Stating the obvious Sunshine is affected by cloud cover and type, more cloud, less Sun.

I suggest the Sun dries the air, which then increases Temperatures.

But of course it depends on the air mass.