Hi guyvaisman,
The fundamental mode of a circular waveguide is the TE11 mode and this mode is double degenerate ( in sinus and cosinus) so the first two modes on HFSS appear to be 90° rotated (mode 1 and mode 2 on your Thumbnails). After, you have TM01 mode that is non degenerate and has a circular symetry (mode 3 on your thumbnail). Then, follow, TE21 , double degenerate sin and cos (mode 4 and mode 5 on your thumbnail). and finally the three degenerate modes , TE01 , TM11 (x2 degenerate in sin and cos) (TE01 mode 6 of your thumbnail).
HFSS give the same exact list of the circular waguide mode than you can find in microwave book. Nethertheless, HFSS don't give the name but only classify the modes by increase cutoff frequencies and after numbered them.
That's all.
Good work in your HFSS simulations.