Forewarn (verb)

1. To give warning or notice in advance.
2. To give prior warning or notice of something, especially danger or trouble.

Origin:

From fore- + warn, meaning to give warning or notice in advance.

Examples:

1. He forewarned us of the storm.
2. The police forewarned residents of the danger.
3. She forewarned her friends of the party's cancellation.
4. He forewarned me of the traffic on the way to the airport.
5. The company forewarned its employees of the upcoming layoffs.