My host has informed me that they need to reboot the server the game is hosted on to apply a security update. It is scheduled for:
2015-12-15 7:00:00 AM UTC
Which is:
2015-12-15 2:00:00 AM EST (server time)
The game will be unavailable during the maintenance. There's a 2 hour window allocated, but the actual downtime may be much less. Hopefully this won't impact too many people as this is usually the least busy time of day for the game.