Can I buy a travel insurance policy if I'm already overseas?

Yes, Americans can buy a World Nomads travel insurance plan when already traveling away from home.

You can be traveling anywhere in the world and buy a trip protection plan. You don't have to be at home or within the USA. 

Your policy can be purchased for the duration you choose (from 1 day up to 180 days) and your policy documents will be sent to you by email.

You should read the Description of Coverage for full details on when cover starts and ends and all other terms, limits, conditions and exclusions of cover.