A short, sudden rain shower — rain that starts quickly and stops soon after (also called a passing shower).
午後はにわか雨があるかもしれないから傘を持って行った方がいい。
There might be a shower in the afternoon, so you'd better take an umbrella.
にわか雨が降ってきて、道がすぐにぬれてしまった。
A sudden shower started and the streets got wet right away.
海辺で遊んでいたらにわか雨に降られて慌てて退散した。
We were playing by the sea when a sudden shower hit us, so we hurriedly left.