late in autumn; late in fall
Fixed literary expression used to describe the deepening of autumn, often in poetic or descriptive contexts.
Late in autumn, the mountains were dyed in autumn colors.
As autumn deepened, the night breeze began to feel chilly.
From 秋 (autumn) + 更けて (the te-form of 更ける, 'to grow late'). The expression is a fixed literary phrase.