Yes, if you are lucky, you can encounter and catch the shiny version of both Thundurus Formes – Incarnate Forme and Therian Forme – in Pokemon GO.
If you defeat Thundurus in a Raid battle, there is a very low chance that you will encounter a shiny version of the Pokemon afterward.
Find out the exact chance of encountering shiny Legendaries in Pokemon GO, so you know roughly how many times you’ll have to defeat Thundurus to catch a shiny version.
If you are after a shiny Thundurus, there is no better time to catch one than during the Pokemon GO Thundurus Raid Hour! After all, the frequency of Thundurus Raids will be significantly increased during this event.

What Does Shiny Incarnate Forme Thundurus Look Like?
Instead of being light blue with dark blue markings, the shiny version of Incarnate Form Thundurus is a violet color with vibrant purple markings, horn, and tail.
The color of the cloud it rides on, as well as the spikes on its tail, are the same as the normal version of this Legendary Pokemon.
While the difference isn’t too great, this shiny is much better than the shiny versions of Tornadus!

What Does Shiny Therian Forme Thundurus Look Like?
The shiny version of Therian Forme Thundurus is a violet color with bright purple markings, horn, and tail. This replaces the light blue and dark blue color scheme of the normal version of this Legendary.
The hair and hands remain white, and the tail spikes stay black for Therian Forme Thundurus’ shiny version.

Of course, Thundurus is just one of the dozens of Legendary Pokemon in Pokemon GO. Most of these Legendaries have shiny versions too!