Video measurements of wave runup were collected during extreme storm conditions characterized by energetic long swells (peak period of 16.4 s and offshore height up to 6.4 m) impinging on steep foreshore beach slopes (0.05–0.08). These conditions induced highly dissipative and saturated conditions over the low-sloping surf zone while the swash zone was associated with moderately reflective conditions (Iribarren parameters up to 0.87). Our data support previous observations on highly dissipative beaches showing that runup elevation (estimated from the variance of the energy spectrum) can be scaled using offshore wave height alone. The data is consistent with the hypothesis of runup saturation at low frequencies (down to 0.035 Hz) and a hyperbolic-tangent fit provides the best statistical predictor of runup elevations.