https://www.gamespot.com/articles/with-fortnite-season-4-near-new-update-adds-emerge/1100-6458495/

For some time now, Fortnite players have speculated that some big event is coming to Battle Royale. The theories have ranged from a meteor--seen in the sky above the game world--crashing into Tilted Towers to some kind of alien invasion. Something is definitely afoot, as evidenced by a new emergency broadcast that's now entered the game.