The Roles of Inner and Outer Rainbands in Secondary Eyewall Formation in a High‐Resolution Simulation of Typhoon Lekima (2019)

This study uses a high‐resolution Weather Research and Forecast simulation to examine the secondary eyewall formation (SEF) in Typhoon Lekima (2019). The model reproduced Lekima's track, intensity changes, and persistent concentric eyewall structure well. Consistent with previous findings, before SEF, the deep‐layer asymmetric inflow and updrafts in the upwind region and descending inflow in the downwind region of the outer rainbands contribute to the expanding tangential wind first in the downshear region through the advection of momentum. The convection in the upshear‐left region is triggered by the convergence induced by the descending inflow in stratiform precipitation of outer rainbands, and enhanced by the phase locking occurring between the radial‐propagating wavenumber‐1 vortex Rossby waves (VRWs) from the primary eyewall and inner rainbands and the azimuthal‐propagating wavenumber‐1 (wavenumber‐2) VRWs at the inner (outer) edge of the developing outer eyewall. The filamentation effect causes the rainband‐associated convection to have a more concentric structure, ultimately leading to SEF. Our findings suggest that the convection generation in the upshear‐left region may be critical to SEF in sheared tropical cyclones (TCs).