If your friend holds a valid US passport he or she is taking it down to the wire - okay as long as he or she returns to the US on or before the passport expires - may be best to re-new now - you never know if there is some major delay or illness or what that might cause the passport to expire.
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Passport ===============
travel information
Sint Maarten============
French West Indies is 6 months from expiry - St. Barths
Anguilla is valid for duration of stay - according to the US State Dept.
