The Shadowlands Castle Nathria raid opens December 8th on Normal and Heroic difficulties. See the raid strategy guide which includes Fatboss videos.

Here's the remaining schedule:

December 15 – Mythic and Raid Finder Wing 1
January 5 – Raid Finder Wing 2
January 19 – Raid Finder Wing 3
February 2 – Raid Finder Wing 4

Note that the minimum item level for Raid Finder is 170.