Many people, including myself, are having troubles logging in. The error we are getting is that the login server is busy and to please try again later. As the message states above, Blizzard will inform us at 1pm PST of any further details.
Those of you who are able to get in, we salute you! The rest of us will wish we were in-game, starting our Feast of Winter Veil activities.
We'll keep you up to date of any further developments.
Update 2:29pm: I and many others are now able to login. No official update at this time. Also, authenticators had nothing to do with it.