The comb jelly Mnemiopsis leidyi is considered one of the world’s most invasive marine species due to its broad ecological and physiological tolerances. The species originates from western Atlantic Ocean, and was first recorded in Scandinavian waters in 2005, yet long-term population trends and environmental drivers in this region remain insufficiently understood. This study examined seasonal and long-term patterns in abundance of M. leidyi on the Swedish Skagerrak coast from 2007 to 2023, and assessed how key environmental variables - i.e. sea surface temperature, salinity, dissolved oxygen, and chlorophyll-a relate to its population dynamics. Abundance and environmental data were obtained from the SHARK database of the Swedish Meteorological and Hydrological Institute (SMHI), and generalised additive models (GAMs) were used to estimate trends and environmental responses. The results showed pronounced interannual variability with alternating periods of high and low abundance of M. leidyi, while the seasonal cycle remained relatively consistent, characterised by low abundance in winter and distinct peaks in late summer to early autumn. Temperature had a strong positive effect on abundance, while salinity showed no significant influence. Dissolved oxygen had a significant but non-linear effect, and chlorophyll-a displayed a weak and uncertain relationship to abundance of M. leidyi. Overall, the findings indicate that M. leidyi responds rapidly to warm conditions. Thus, ongoing ocean warming may facilitate its future establishment and ecological impact in northern cold-temperate waters.