Observed rainfall asymmetry of tropical cyclones in the process of making landfall in Guangdong, South China

This study investigates the rainfall asymmetry of tropical cyclones (TCs) during landfall in Guangdong (GD), South China, using satellite-based, gauge-satellite merged, and reanalysis precipitation datasets. We examine the characteristics of TC rainfall asymmetry, its primary controlling factors, its evolution during landfall, and potential variations across different El Niño–Southern Oscillation (ENSO) phases.

The results demonstrate that vertical wind shear (VWS) dominates TC rainfall asymmetry in GD, with the rainfall maximum consistently located in the downshear left of VWS. Since most TCs are associated with southwesterly VWS, the peak rainfall typically occurs in the south to southwest sector relative to the TC center. This feature persists across all summer months (June–September) and is consistent among TCs of varying intensities, including tropical depressions (TD), tropical storms (TS), severe tropical storms (STS), Typhoons (TY), and super typhoons (STY). In contrast, storm motion shows no significant influence on rainfall asymmetry in GD.

Despite a reduction in rain rate during landfall, the TC rainfall asymmetry remains remarkably stable, with no substantial changes in either the phase or amplitude from 24 hours before to 12 hours after landfall. The rainfall maximum persistently aligns with the downshear left of VWS, and the asymmetry magnitude remains approximately 50%, indicating that asymmetric rainfall accounts for nearly half of the total TC rainfall. Furthermore, no statistically significant differences in rainfall asymmetry are found among El Niño, La Niña, and neutral ENSO phases.

These findings enhance the understanding of TC rainfall distribution and provide valuable insights for improving rainfall forecasts in GD, particularly for extreme precipitation events associated with landfalling TCs.