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sudden; abrupt; unexpected; immediate; hasty; improvised; impromptu; offhand
impromptu skit
bandwagon fan; fair-weather fan
にわか雨が降ってきたので軒下で雨宿りした。
A sudden rain started, so I took shelter under the eaves.
にわかには信じられない話を聞かされた。
I was told a story that was hard to believe right away.
にわかに風が強くなり窓を閉めた。
The wind suddenly picked up, so I closed the windows.