Antarctic sea–ice reached a record low in 2023, with pronounced atmospheric and oceanic responses across both polar and midlatitude regions. Using ERA5 reanalysis data and an objective cyclone tracking algorithm, we identify a sharp decline in extratropical cyclone (ETC) frequency over the South Atlantic during austral autumn 2023, particularly in the midlatitudes of the South Atlantic (MLSA) and the southern Weddell Sea (SWS). In the MLSA, thermodynamic forcing from Weddell Sea surface warming suppressed cyclogenesis by reducing lower-tropospheric baroclinicity through two pathways: a weakened meridional temperature gradient and enhanced static stability. The SWS decline was dynamically driven by a Zonal Wave 3 pattern, where anomalous northerly flow suppressed katabatic wind convergence, inhibiting cyclonic circulation. These region-specific mechanisms resulted in a basin-wide decline in South Atlantic ETC frequency, leading to a decrease in associated extreme precipitation and strong wind events. However, a paradoxical increase in poleward moisture transport was observed at high latitudes (65°S–70°S), as anomalous northerly winds steered cyclones from lower latitudes rapidly poleward, minimizing moisture loss along their tracks. Our findings demonstrate a thermodynamic linkage between intense autumn polar warming and reduced midlatitude ETC frequency, underscoring the importance of ice–ocean–atmosphere coupling in shaping not only the frequency of midlatitude storm systems but also their downstream impacts.