Is a passport required to re enter the US from St Thomas?

No. Even with the new Western Hemisphere initiative effective June 1, 2009, travel directly from the US to a US territory does not require a passport.

Please read the following for more info: http://www.travel.state.gov/travel/cbpmc/cbpmc_2223.html http://www.dhs.gov/xtrvlsec/crossingborders/index.shtm