<p>We investigate the modulation of land–sea breeze circulation and rainfall formation by tropical peat islands along the east coast of Sumatra using combined observational and theoretical approaches. Observations from a compact X-band polarimetric radar deployed on Bengkalis Island, together with a two-dimensional linear analytical model based on the Green’s function method, are used to examine the diurnal evolution of convection. Results reveal a robust diurnal rainfall cycle, with precipitation maxima occurring in the afternoon and around midnight. Analytical simulations indicate that peat islands enhance surface thermal contrasts and strengthen low-level convective responses, particularly during the morning and evening transition periods. These convective responses modulate the inland-to-coastward propagation of convective clouds. When moisture condensation induced pressure anomalies are incorporated into the model, enhanced zonal flow and vertical moisture convergence emerge over peatland regions. The results suggest that land–biosphere-induced pressure gradients associated with tropical peat forests play an important role in intensifying local convection and rainfall over coastal environments.</p>