Observations from six Lagrangian Surface Wave Instrument Float with Tracking (SWIFT) drifters in January-February 2020 in the northwestern tropical Atlantic during the Atlantic Tradewind Ocean-atmosphere Mesoscale Interaction Campaign (ATOMIC) are used to evaluate the influence of wave-current interactions on wave slope and momentum flux. At wind speeds of 4-12 m/s, wave mean square slopes are positively correlated with wind speed. Wave-relative surface currents varied significantly, from opposing the wave direction at 0.16 m/s to following the waves at 0.57 m/s. For a given wind speed, wave slopes are up to 20% higher when surface currents oppose the waves compared to when currents strongly follow the waves, consistent with a theoretical Doppler shift between the absolute (fixed) and intrinsic (relative) frequency. Assuming an equilibrium frequency range in the wave spectrum, wave slope is proportional to wind friction velocity and momentum flux. The observed variation in wave slope equates to up to a 40% variation in momentum flux for a given wind speed. This is 30% greater than the variation expected from current-relative winds alone, and suggests that wave-current interactions can generate significant spatial and temporal variability in momentum fluxes in this region of prevailing trade winds. Results and data from this study motivate the continued development of fully coupled atmosphere-ocean-wave models.