Thunderstorm Canyon is more of a gorge than a canyon. It starts with an impressive 40m abseil but then opens out a bit shortly afterwards.
It was discovered in November 1977 on a joint SUBW-Ramblers trip, and was named as there was a thunderstorm as the party was rigging the first abseil.
Thunderstorm Canyon is most obviously done from the Mt Cameron Track, on the east side of Rocky Creek. However, it is probably an easier and more worthwhile day to do it from Closet Canyon, on the west side of Rocky Creek.
From the junction of Closet Canyon and Rocky Creek, head downstream for 200m to the next creek on the right, which is the creek with Thunderstorm in it. Climb the point to the south. There may be a tape near the bottom to get up the first difficult bit. The rest has the odd tricky bit, but it is not particularly exposed until the last pitch, which is very exposed. Head up to the next cliff line, and along to the left under the cliffs. Watch the gullies on your side and the other side and drop down to the creek at MGA501164 (AMG500162, Rock Hill). The first abseil is only a short distance downstream.
The main abseil is 40m. The pulldown can be difficult, and it is possible for the last person to rerig at a lower tree. Then there is a short abseil or climb down. The canyon opens out into a deep gorge, and it is an easy walk back to the Rocky Creek junction.
As for Closet Canyon.