A double experience weekend will be in effect from Saturday, September 1 through Monday, September 3. It was announced on the forums:

Greetings intrepid gamers,

For the many of you asking the question, yes, we will be having a double XP weekend for this upcoming holiday.  We have it scheduled from 12:01 AM Saturday until 11:59 PM Monday. 

We hope you have a wonderful weekend!

Holly "Windstalker" Longdale
Producer
EverQuest II