In game announcements have let us know there will be rolling restarts tomorrow morning. The restarts will happen at 5:00 a.m. PST / 8:00 a.m. EST. Each realm is usually down for only 15 minutes.
There will be additional realms that will be down for longer maintenance. Currently Tichondrius and Proudmoore are listed as needing to be down for an extra hour. Additional realms will eventually be listed on the official Service Status Forums, although nothing is up there just yet.
We'll update this post, and keep you updated throughout Tuesday morning if this turns into anything else other than just a restart.