As someone who's living in a humid tropical climate, i'd advice the OP to wear an undershirt, regardless of the fabric he'll eventually choose. At those temperatures you're gonna sweat anyway, so better to have an extra layer to absorb that moisture. Helps prevent your shirt become all wrinkly.
Stitchy, I'm gonna try but I'm not sure if I can make it this week. If not, will I be allowed to enter a fit that I already posted on WAYWRN last week? (Say, if you feel you haven't got enough entries for the FC...)