somewhat sudden
An expression used to describe something that happens with a degree of suddenness, often implying it is not entirely unexpected or is less abrupt than 突然 alone. It can carry a nuance of 'a bit sudden' or 'rather sudden'.
His retirement was somewhat sudden, but there had been rumors for a while.
It was a somewhat sudden rain, and I didn't have an umbrella.
Compound of 突然 (sudden) and 目 (a suffix that can indicate a degree or tendency). The exact derivation is uncertain, but it likely developed as a colloquial way to express a moderate degree of suddenness.