Analysis of the Cause and Radar Characteristics of a Rare Autumn Strong Tornado Process Occurred in Northern Jiangsu Province

On September 19, 2023, a rare autumn tornado outbreak, consisting of three successive tornadoes (including one EF3), occurred in northern Jiangsu, China, causing significant damage. This study presents a comprehensive analysis of this event using multisource data, including Doppler radar, ERA5 reanalysis, and surface observations. We find that pretornadic mesoscale vortices were triggered and intensified during the eastward movement of the Jianghuai cyclone, along low‐level shear lines on the warm side of a quasi‐stationary mesoscale front. The synoptic environment was characterized by an anomalously strong and persistent subtropical high, which provided record‐breaking moisture (precipitable water >66 mm) and instability (CAPE >2200 J kg −1 ), coupled with extreme low‐level wind shear (>18 m s −1 in 0–1 km). These conditions created a classic yet extreme setting for tornadic supercells. At the storm scale, the tornadoes formed during the merging and intensification of multicell thunderstorms. Radar analysis revealed that the two strongest tornadoes (EF2 in Nancai and EF3 in Funing) exhibited clear supercell characteristics, including hook echoes and tornado vortex signatures (TVSs). Tornadogenesis in both cases coincided with the peak values of low‐level differential velocity (LLDV exceeding 40 m s −1 ). The Funing EF3 tornado was further confirmed by a prominent tornado debris signature (TDS) in dual‐polarization radar data. A key advance presented here is the identification of a hybrid tornadogenesis mechanism. While the storms displayed classic supercell dynamics (tilting and stretching of vertical vorticity), the process was significantly enhanced by the amplification of pre‐existing horizontal vorticity along successive, evolving meso‐β‐scale convergence centers. This mechanism, which shares characteristics with both supercellular and landspout processes, explains the sequential development of this “tornado cluster.” Our results underscore that in high‐shear, high‐instability environments, detailed analysis of mesoscale boundaries are crucial for anticipating tornadogenesis. This study enhances the understanding of autumn tornado outbreaks in eastern China and provides insights for improving monitoring and warning strategies for such rare but high‐impact events.