I don't know if there's a scientific term for the difference between the daily maximum temperature and the daily minimum temperature, but this gap seems to be quite great in Bulgaria.
When I get up in the mornings it is a brisk 10 degrees Celsius, and I need to wear a jacket to work. But by mid-afternoon, it is a warm 31 degrees, even warmer than it is currently in Israel. But in Israel you don't have such a big temperature gap.
The other thing about the high temperature in Bulgaria during September is that it is really just a peak. Even when the afternoons are quite warm, the mornings remain cool and nice. The maximum temperature is reached for a short period, and then the day begins cooling again.
All this won't last long, as the Autumn is here with falling leaves covering the ground. Cooler and colder days are ahead.