Johnston Atoll

http://en.wikipedia.org/wiki/Johnston_Atoll

A group of four small islands with a total area of 2.67 km², it was used by the US during WW2. After that activity gradually subsided. There is a runway occasionally used for emergency situations. Officially it is another refuge now.

Potential:

Again, a few small islands with a large coral reef platform, already considerably expanded by dredging. It is proven to be able to house large numbers of people; but the resources and food were all imported then. No water source.