beginning of autumn; early autumn
Refers to the period when autumn is just starting, typically around September in Japan. Often used in weather forecasts, seasonal greetings, and descriptions of seasonal changes.
In early autumn, the mornings and evenings become cooler.
Typhoons often come in early autumn.
When early autumn comes, the mornings and evenings turn cool.
The early-autumn breeze still carries a bit of summer heat.
I'm planning to travel in early autumn.