Trade-wind cumuli play a crucial role in Earth’s energy budget due to their prevalence and net cooling effect. How these shallow clouds respond to a warming climate remains a key uncertainty for climate projections. The Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) provided a unique opportunity to investigate how relatively weak yet ubiquitous mesoscale sea surface temperature (SST) features impact trade cumulus cloudiness. This poster will present complementary investigations using ATOMIC-validated satellite observations and a cloud-resolving Large Eddy Simulation (LES) Model. Composite analysis of the satellite observations shows in-phase modulations of daily mean cloudiness over weak sea surface temperature anomalies (0.25 K on average). These daily cloudiness anomalies are positively correlated with the 10-m neutral surface wind speed but are offset from the near-surface wind convergence. Idealized LES experiments conducted with the mean large-scale environmental conditions during ATOMIC reproduce these satellite composite results. LES results further suggest that the enhanced cloudiness signal over SST warm patches in the satellite composite mainly reflects enhanced cloudiness near the cloud base below 1 km. LES results also show that the increased low-level cloudiness is driven by locally enhanced turbulence instead of by surface convergence-induced upward motions. How enhanced turbulence drives cloud formation will be explained further. The relative roles of enhanced surface sensible and latent heat flux over SST warm spots in initiating trade cumulus generation will be shown based on mechanism denial experiments.