Now a Coach wrote:
If it was 27 degrees C with 70% humidity in the UK every summer you'd be taking your shirts off too.
The picture linked looked like it was in the fall.
I'll take my shirt off on hot days for a run most times.
I wouldn't do it in a race mostly because it looks improper in a public setting with many people together.
There should be some sense of formality there.
I have a number of T shirts but few singlets to wear when it's hot.
So taking my T shirt of for a run on a hot day works.