Relative humidity is the comparison between amount of moisture in air to the amount of air it can hold.
Moisture in air are stored in the space between two air particles,and heat energy is stored in the surface of the air particles as the temperature increases then the space between air particles increases.
If, so then in a particular area the amount of air pockets decreases but as they have expanded they should have a large space.
Less the air particles then less the relative humidity if temperature increases.
And vice versa to the temperature drop, air gets cooled and it leads to an increase accumulation of more air pockets in an area.
More the air pockets more the relative humidity.