suddenly; abruptly; unexpectedly
Describes a sudden, often surprising change or occurrence. Commonly used in the phrase にわかには信じがたい (hard to believe suddenly).
空がにわかに曇って、雨が降り出した。
The sky suddenly clouded over and it started to rain.
I couldn't believe the news all of a sudden.
The weather suddenly changed and it started to rain.
His story is hard to believe right off the bat.
The sky suddenly clouded over and the wind picked up too.