The Asian summer monsoon (ASM), which undergoes two distinct stages of abrupt transitions, resulting in successive onsets from mid‐May to early June, accompanies an abrupt temperature increase in the upper troposphere around the Tibetan Plateau (TP). However, observation studies showed that cumulus convective activities become less frequent at the onset phase of the ASM, indicating the contribution of a heat source other than the surface heating of the TP. The mechanism of upper tropospheric warming is investigated using the climatology derived from the reanalysis data. Heat budget analysis of the upper troposphere revealed that adiabatic subsidence plays an important role in the temperature increase from late April to mid‐June. We suggest that the significant upper level convergence and adiabatic warming to the southwest of the TP is closely associated with the anomalous Hadley circulation. The significant divergent flow from the tropical convection induces upper level convergence and adiabatic subsidence dominating radiative cooling. Furthermore, the downdraft branch of the Hadley‐type circulation to the southwest of the TP is localized and enhanced owing to the divergence over adjacent regions such as the TP, the Indochina Peninsula, and southern China. The atmosphere over the TP is thus heated not only by diabatic heating from the surface, but also by the adiabatic subsidence in the upper troposphere around the onset phase of the ASM. We have verified this by numerical simulations, which show that the latent heat flux around the Bay of Bengal, which forms the deep convective activity and upper circulation, contributes significantly to the upper tropospheric warming.