Many know, not to wash a car in direct sunlight, especially dark coloured cars.
Main reason, panel temperature.
Today is especially hot, by British weather standards that is.
So 22C in direct sunlight on a silver or light coloured car can be around 25-35C, on dark coloured cars, it can be 70C upwards and applying water to a car that hot can cause a steam haze.
I had agreed to wash a colleague’s car the other day, today she brought it down and got lucky that even though the car is a black Peugeot the panels weren’t too hot so tackled it quickly and used Adam’s H2O Guard & Gloss to dry and seal. The paint is pretty messed up as it hasn’t been looked after AT ALL which isn’t unexpected on a 12 year old run about.
The car is not as bad as a 20/20, more a 10/10. She looks good doing 10mph from 10' away.