Understanding the Diversity of Shear-Relative Convective Patterns of Rapidly Intensifying Tropical Cyclones

Abstract The convective pattern of tropical cyclones (TCs) relative to vertical wind shear (VWS) is an important indicator of rapid intensification (RI), yet significant variability exists among RI TCs, which can make effective predictions of RI onset challenging. In this study, a self-organizing-map clustering method is employed to classify shear-relative convective patterns at RI onset. Four distinct clusters are identified: one fairly symmetric pattern with a compact core (SYM, 26% of all cases) and three asymmetric patterns with peak convection upshear left (USL, 25%), downshear left (DSL, 32%), and downshear right (DSR, 17%). An objective asymmetry index reveals that RI in SYM and USL follows significant precipitation axisymmetrization, whereas DSL and DSR experience RI after sharp increases in asymmetric precipitation. Environmental analyses indicate that SYM intensifies under lower VWS and resultant weaker ventilation. USL experiences moderate VWS, with precipitation axisymmetrization favored by increased right-of-shear latent heat flux (LHF) associated with an anomalous large-scale gyre. DSL, with relatively stronger VWS, experiences asymmetric convective intensification favored by increased midlevel relative humidity, LHF, upper-level divergence, and lower-level inflow downshear or left of shear. DSR, despite moderate VWS, has the most favorable environment, and its unique convective distribution at RI onset is influenced by an anomalous large-scale vorticity dipole downshear, a right-of-shear low-level mean flow, and the associated LHF anomalies. These findings highlight the environmental origins of the diverse convective patterns of RI TCs, underscoring the need to account for intercase variations in convective and environmental properties in future statistical models. Significance Statement The convective pattern of tropical cyclones (TCs) relative to vertical wind shear plays a crucial role in their rapid intensification (RI). Despite various reported shear-relative convective patterns, a systematic classification has yet to be established. This study employs a self-organizing map clustering method to identify four distinct shear-relative convective patterns at RI onset: one relatively symmetric pattern and three asymmetric patterns with the strongest convection in different shear-relative quadrants. Each cluster is linked to unique dynamic and thermodynamic environmental configurations that drive diversities in convective patterns. These findings deepen our understanding of the interplay between convection, environmental factors, and RI, highlighting the need to account for intercase variations in convective and environmental properties in future statistical models for RI forecasting.