You cannot choose to vote in a state without first establishing residency there. As a U.S. citizen living overseas, your last U.S. residence address is your "voting residence address" (your address for voting purposes). To establish a new voting residence address you must live in the new location with an intent to make that location your home.
To see the residency requirements of each state, visit our State Voting Requirements page. Choose your state, and on the following page select your voting location and "Eligibility Requirements."