Window misting

[pandaman]

I know others have mentioned window misting in a double glazed window but I have a south facing bathroom window in a 30 yr old house. I know the seal has gone but cannot understand why condensation forms in the heat waves we have been getting. It mists up part of the window and actual drops can be seen running down the glass and pooling along the bottom. Why does it do this in heat we have been having with the sun shining on the glass?

 

[Wayners]

There is silica in the outside of window all the way around that gets saturated eventually so that maybe leaking moisture back inside pain.
Water will form inside.

Also it's high humidity in the air as car is wet every morning.
Physics question I guess