Results are reported from an improved measurement of nu(mu) -> nu(e) transitions by the NOvA experiment. Using an exposure equivalent to 6.05 x 10(20) protons on target, 33 nu(e) candidates are observed with a background of 8.2 +/- 0.8 (syst.). Combined with the latest NOvA nu(mu) disappearance data and external constraints from reactor experiments on sin(2) 2 theta(13), the hypothesis of inverted mass hierarchy with theta(23) in the lower octant is disfavored at greater than 93% C.L. for all values of delta(CP).