Analysis of convective activity in Tropical Storm Delta in a warmer climate

Under future climate change scenarios, warmer ocean conditions are expected to substantially modify the behavior of tropical cyclones, particularly in regions where these systems are currently uncommon. In this work, tropical storm Delta (2005), which developed in the northeastern Atlantic basin, is used as a case study to explore how elevated sea surface temperatures influence cyclone intensity, internal convection, and the characteristics of its extratropical transition. Using high-resolution HARMONIE-AROME simulations, a reference experiment of the storm with boundary and initial conditions from ERA5 is compared with a warmer scenario in which sea surface temperatures are increased. The simulations reveal that enhanced surface heat fluxes strongly reinforce convection in Delta’s eyewall in a warmer scenario, promoting more vigorous and sustained updrafts, driving a marked deepening of the cyclone during its tropical stage. This intensification allows Delta to reach hurricane intensity. Later, the transition to an extratropical system begins earlier, extends over a longer period, and evolves into a more severe system. These changes translate into substantially stronger impacts over the Canary Islands (Spain), particularly through extreme wind gusts during the post-tropical stage. The findings underline the potential for anthropogenic climate change to increase the severity of storms with tropical features affecting western Europe, with important implications for future risk assessment in the region.