This manuscript presents a study of oceanic diurnal warm layers in kilometer-scale global coupled simulations and their impact on atmospheric convection in the tropics. With the implementation of thin vertical levels in the ocean, diurnal warm layers are directly resolved, and sea surface temperature (SST) fluctuations of up to several Kelvin appear in regions with low wind and high solar radiation. The increase of SST during the day causes an abrupt afternoon increase of atmospheric moisture due to enhanced latent heat flux, followed by an increase in cloud cover and cloud liquid water. However, although the daily SST amplitude is exaggerated in comparison to reanalysis, this effect only lasts for 5-6 hours and leads to an absolute difference of 1% for cloud cover and 0.01 kg m-2 for cloud liquid water. All in all, the impact of diurnal warm layers on convective cloud cover is found to be negligible in the tropical mean.