first strong wind of autumn
A seasonal word (kigo) in haiku and traditional poetry, referring to the first powerful wind that signals the arrival of autumn.
初嵐が吹いて、木の葉が一斉に散り始めた。
The first autumn gale blew, and the leaves began to fall all at once.
Compound of 初 (hatsu, 'first') and 嵐 (arashi, 'storm'). The exact historical origin is uncertain, but it is a traditional seasonal term in Japanese poetry.