ArenaNet has kept its lips sealed about any further details, and they continue to do so but with the event soon approaching they have released an event schedule without giving away any spoilers:
On Friday November 16th at noon PST (20:00 GMT) the weekend will kick off with an Event in Lion’s Arch that you don’t want to miss. This will trigger events in other parts of Tyria as well.
On Saturday November 17th at noon PST (20:00 GMT), another phase will kick in.
Each phase is triggered by a special event, but you will be able to enjoy additional content afterwards even if you cannot make the kick-off time. There is one exception:
The event will culminate in a big Finale on Sunday November 18, make sure you will not miss it. This will be a onetime only event chain that will run multiple hours, and it will kick off at noon PST (20:00 GMT). Again, this will only run once, so make sure you will be there! There will be plenty of content available to enjoy that will remain permanently in the world as a result of the outcome of this event on Sunday.
The event was first announced in November and has been hyped about since. The schedule is just a reminder to make sure everyone is on the same page, and no one misses out. More details will be updated as the event gets closer so keep an eye on the Guild Wars 2 forums.
Source: Guild Wars 2