The really hot days and nights in Adelaide are due to Northerly Winds off the desert in the centre of Australia.
By definition deserts are dry and hot and the air coming off them is therefore dry and hot.
Any winds we get from the West and South are automatically cool because they pass over the ocean.
It is just the way it is here. I've lived in Adelaide for 60 years and as far as I know we have never had a 37C day with high humidity. It is always low humidity when it is hot. We would all probably die if a high humidity hot day ever happened. :)
You are welcome to look through previous Adelaide summers on the BOM site and prove me wrong by finding a 37C day with 50% humidity in the Adelaide records. Good luck. :)
Most Adelaide people would simply accept we have low humidity when it is hot.
What Adelaide folk might call a "high humidity" day would have a Queenslander splitting his sides with laughter.
For example, _any_ 25C day in Adelaide is just a beautiful and very pleasant and comfortable day.
A perfect day every time it is 25C.
People in Queensland couldn't ever say that.
Ross