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.