Definition from Wiktionary, the free dictionary
- (transitive) to serve as a warning or omen
- A kingdom they portend thee, but what kingdom, / Real or allegoric, I discern not; Nor when: eternal sure--as without end, - John Milton, Paradise Lost
- (transitive) to signify; to denote
- Let it be known that the Rapture portends the End of Days.
- 2012 June 26, Genevieve Koski, “Music: Reviews: Justin Bieber: Believe”, The Onion AV Club:
- When the staccato, Neptunes-ian single “Boyfriend” was released in March, musical prognosticators were quick to peg the album it portended, Believe, as Justin Bieber’s Justified, a grown-and-sexy, R&B-centric departure that evolved millennial teenybopper Justin Timberlake into one of the unifying pop-music figures of the aughts.
Related terms 
to serve as a warning or omen