I'm planning on moving the site to its new server late this evening.
To ensure no posts are lost, the current (old) server will be taken off-line once the migration begins. Once everything has been transferred, the old server will remain off-line and, as the changes take hold throughout the internet (a process you can speed up by restarting your router), members will automatically start using the new server.
For most people, everything should be back to normal by the morning.