https://www.gamespot.com/articles/fortnite-servers-go-offline-for-season-5-update/1100-6460325/

The release date for Fortnite Season 5 is finally upon us, and that means another big patch is being rolled out. As part of the update process, the game's servers have gone down for an indefinite amount of time while developer Epic Games introduces the new content. Once the staging is all finished the Season 5 changes will finally be revealed.

As indicated in a tweet from Epic Games, the server downtime started on July 12 at 4 AM ET / 1 AM PT / 8 AM GMT adn it's unclear how long the process will take. In a linked Reddit thread, the team also noted that this patch will be larger than normal, and recommends checking to make sure your auto-update settings are on. Plus, be prepared for possible slow download speeds, and save any content you want from your existing replays.