If the Islands did not sink chances are they were nuked off the map. Naval Bases such as pearl harbour and its also America's main operations center in the pacific ocean. If 77 nukes were for southern Nevada I can imagine several hundred for a target like Hawaii. Being volcanic that many nukes should do something earth shattering and make it sink.
Oahu would be obliterated, or at least close to it. It has the military bases and the major population centers so it would probably get the bulk of the nukes - and honestly it isn't a very large island. Technically the volcanoes are extinct but that wouldn't necessarily stop Science! from providing a fiery aftermath. The Big Island and Maui would be the next most important targets and they are also volcanically active so they'd no doubt have massive eruptions - anyone not killed in the nuclear blast or the initial eruptions would likely get driven in to the ocean by the lava flows. The other islands may escape special treatment - but even if they weren't nuked directly they'd still be badly affected by their neighbors.
An aside about Nevada, while modern Las Vegas may not seem like a prime target in the Fallout universe Mr. House's presence probably raised it's profile considerably. Even with this consideration Hawaii would undoubtedly be a higher priority, it would no doubt still be a military hub for America's interests in the Pacific, I just don't think we should downplay Las Vegas' importance.