Abstract We analyse 17 Mediterranean cyclones with tropical‐like characteristics using European Centre for Medium‐Range Weather Forecasts (ECMWF) Reanalysis Version 5 (ERA5) reanalysis data to investigate the role of upper‐tropospheric processes and their seasonal variations in cyclone development. Our results show that cyclones occurring in September exhibit the most intense convection, with Ianos , one of the strongest medicanes on record, representing an extreme case. Using correlation coefficients between and upper‐level relative humidity () and potential vorticity (), we find that warm‐core strengthening is systematically linked to upper‐tropospheric moistening. While is generally negative, consistent with diabatic erosion/decoupling of the upper‐level PV anomaly during warm‐core growth, both its magnitude and the level of maximum anticorrelation vary across cyclones. Using back‐trajectory analyses, we investigate the presence of dry intrusions in the early and mature cyclone phases. We show that one or more dry intrusions are common in medicanes, with an intensity that is case‐dependent. Consistently, 700‐hPa equivalent potential temperature () fields show that descending trajectories correspond to low‐ filaments wrapping around the cyclone, and that a warm‐seclusion‐like structure is visible during warm‐core onset. While dry intrusions can accelerate warm‐core formation by favouring convection, the eventual warm‐core intensity depends critically on diabatic processes near the cyclone centre, as exemplified by Ianos . In fact, despite only marginally descending flows before the main tropical‐like phase, this cyclone develops the strongest warm core among the cyclones analysed. This motivates us to examine Ianos in detail using ERA5 and a Weather Research and Forecasting (WRF) simulation with a grid spacing of 3 km, which confirms the need for high resolution to represent the cyclone intensity correctly, highlights the dominant contribution of diabatic heating to cyclone deepening, and suggests a secondary role of the weak descending branch of the PV streamer.
Nigro et al. (Wed,) studied this question.