Extreme Humid Heat during South Asian Summer Monsoon Breaks

Wet bulb temperature is a combined metric of air temperature and humidity, strengthening its measurement and prediction of heat stress compared to temperature alone. Extreme wet bulb temperatures are thus multivariate extremes with direct societal implications, and understanding what controls their occurrence is critical to preparing for the associated negative human health and socioeconomic impacts. Previous literature has suggested that the most extreme humid heat events in South Asia take place during the pre-monsoon season immediately preceding sustained precipitation onset. Building off of previous research which has identified humid heat extremes during the absence of convection in otherwise hot and humid environments, we explore whether extreme humid heat events tend to occur during monsoon breaks in South Asia. Initial results identify widespread positive wet bulb temperature anomalies during monsoon breaks of sufficient length in the eastern part of the subcontinent. These positive anomalies are particularly pronounced in the last day of the monsoon break, before the following active phase is established. Physical mechanisms controlling the evolution of these wet bulb temperature extremes during monsoon breaks of various lengths are explored. Improving understanding of extreme humid heat timing in South Asia during the monsoon season is essential to evaluating the safety of outdoor labor in the present and future climate.