This is the 2097th most frequent German word.
warnte
"Warnte" means "warned."
In this sentence, 'warnte' is used to indicate that the subject ('Sie') made someone else aware of a potential hazard or threat.
Sie warnte mich vor der Gefahr.
She warned me about the danger.
Here, 'warnte' describes an act of informing or cautioning by an entity (the news) about adverse conditions.
Die Nachricht warnte uns vor schlechtem Wetter.
The news warned us about bad weather.
In this usage, 'warnte' is employed to convey a caution or advice given by the subject ('Er') regarding an action (not coming late).