What does this idiom mean?

"Autumn is contending for summer heat" refers to the time from beginning of autumn to summer heat. Although it feels like autumn, the heat of summer is still unabated. During this period, the weather is often cool in the morning and hot in the afternoon, with a large temperature difference between morning and evening, and there may be weather changes such as storms at noon. People will also show the alternation of seasons, wearing cooler summer clothes in the morning and evening, and may need to change into cooler autumn clothes at noon. This idiom is mainly used to describe that the temperature drops gradually in early autumn, but it still retains the characteristics of hot weather in summer.