Wet-bulb temperature extremes (WTEs) occur due to a combination of high humidity and temperature, and are hazardous to human health. Alongside favourable large scale conditions, surface fluxes play an important role in WTEs, yet, little is known about how land surface heterogeneity influences them. Using a 10-year, pan-African convection-permitting model simulation, we find that most WTEs have a spatial extent < 2000 km2. They occur preferentially over positive evapotranspiration and soil moisture anomalies (SMA) typically following rainfall. The wet-bulb temperature is locally amplified by 0.5-0.6 °C in events associated with smaller-scale SMA compared to events with larger-scale SMA. A mesoscale circulation, resulting from stronger spatial contrasts of sensible heat flux, more efficiently concentrates moist, warm air in a shallower boundary layer. This amplifying mechanism could explain the underestimation of peak Twb values in coarser-resolution products. The robust link with antecedent SMA and previous rainfall may help issue localized early warnings.