Abstract. The Arabian Sea (AS) and the Bay of Bengal (BoB) are the major part of the Indian Ocean where cyclonic activities prevail each year, resulting in extreme precipitation events, particularly during the pre-monsoon season. Despite the significance of cyclones in Nepal, no studies have investigated their impact on the isotopic composition of atmospheric water vapour (δ18Ov, δDv, and d-excessv). Here, we present the results of continuous measurements of the isotopic composition of atmospheric water vapour at Kathmandu from 7 May to 7 June 2021 during two pre-monsoon cyclone events, namely cyclone Tauktae formed over the Arabian Sea, and cyclone Yaas formed over the Bay of Bengal. We observed a significant depletion of δ18Ov and δDv during both cyclone events compared to before and after the cyclone events which was attributed to changes in moisture sources (local vs. marine) as inferred from backward moisture trajectories. The outgoing longwave radiation (OLR) and regional precipitation during cyclone events together with the observed correlation between vertical velocity and δ18Ov showed high moisture convergence and heavy convection at and around the measurement site which caused unusually depleted δ18Ov during that period. Moisture convergence and convection were stronger during cyclone Yaas which resulted in higher (lower) d-excessv (δ18Ov), compared to Tauktae, possibly due to strong downdrafts during the cyclone-related rain events which can transport vapour with higher (lower) d-excessv (δ18Ov) toward the surface. Our study reveals that tropical cyclones that originated from the BoB and the AS modulate isotopic signals of near-surface atmospheric water vapour considerably in Nepal. Hence caution should be made while interpreting the isotopic variability during the non-monsoon season and the effect of cyclones on the isotopic composition of precipitation and atmospheric water vapour. Our results shed light on key processes governing the isotopic composition of atmospheric water vapour at Kathmandu and may have implications for the paleoclimate reconstruction of tropical cyclone activity.