1Sudden; abrupt; unexpected; hasty; improvised. Often written in kana as にわか.
にわか雨が降ってきたので、傘を差した。
A sudden shower started, so I opened my umbrella.
にわか仕立ての演出だったが、盛り上がった。
It was an improvised performance, but it got lively.
2An impromptu skit or comic performance (often referred to as にわか狂言). Sometimes written as 仁輪加.
祭りでにわかな芝居が披露された。
An impromptu play was presented at the festival.
3A fair-weather or bandwagon fan; someone who becomes a fan only temporarily or superficially.
最近になってにわかファンが増えている。
Bandwagon fans have been increasing recently.