This is the 2098th most frequent Polish word.
niespodziewanie
Unexpectedly.
The adverb 'niespodziewanie' is used here to indicate that the rain began in an unanticipated manner.
Niespodziewanie spadł deszcz.
Unexpectedly, it started raining.
Here, 'niespodziewanie' emphasizes the unplanned nature of the visitors' arrival.
Przyjaciele niespodziewanie mnie odwiedzili.
My friends visited me unexpectedly.
In this context, 'niespodziewanie' highlights that the message about the promotion was a surprise.