Someone in the Guild "of the Sun" was asking the other day. Stumbled upon this info whilst looking up leather farming.
ISLE OF THUNDER
To get to the Isle of Thunder, you have to get the quest called the "Thunder Calls" from Lyalia (Alliance-Shrine) / Sunwalker Dezco (Horde-Shrine). The quest will lead you to the "The Storm Gathers" quest in Townlong Steppes, once you speak to the NPC there, you will fly to the Isle of Thunder. Next time you come here, there will a portal to the isle and you won't have to talk to the NPC.