It should be fully compatible with this camera as stated in the Tamron webpage for this lens "Tamron Di lenses are performance optimized for digital SLR cameras and usable with DSLRs featuring sensors commonly referred to as APS-C, measuring approximately 24mm x 16mm, as well as larger full frame (36mm x 24mm) sensors and 35mm film SLRs." From Nikon's website the image sensor on the D7100 is 23.5 x 15.6mm http://www.nikonusa.com/en/Nikon-Products/Product/Digital-SLR-Cameras/1513/D7100.html#tab-ProductDetail-ProductTabs-TechSpecs.
You have to wait till the D7100 comes out and try it. Not all the current third party lenses can operating 100% of the new camera. This is the reason I stick with Nikon lenses even have to pay more (for the compatibility for future new camera). but do not get discuraged just try it when the D7100 comes out.