During the "Triple Transit" we will see three shadows on Jupiter's disk at the same time. The shadows of Io, Europa and Callisto will all fall on the visible side of Jupiter at the same time. After the shadows of Io and Europa move off the edge a true double transit will take place.
These events are rare so go out and enjoy this one, I have never seen a triple transit since I started to observer Jupiter back in 2007.
All times are in UTC and you will need to convert to your local timezone. I hope these screenshots and animations help your planning efforts and clear skies to you.
A link to the individual screenshots are here: https://plus.google.com/photos/108750361778865447048/albums/5933194308670906897?banner=pwa