Predictability and dynamics of the rapid intensification of Super Typhoon Lekima (2019)

This study explores the effect of the initial axisymmetric wind structure and moisture on the predictability of the peak intensity of Typhoon Lekima (2019) through a 20-member ensemble forecast using the WRF model. The ensemble members are separated into Strong and Weak groups according to the maximum 10-m wind speed at 48 h. In our study of Lekima (2019), the initial intensity defined by maximum 10-m wind speed is not a good predictor of the intensity forecast. The peak intensity uncertainty is sensitive to the initial primary circulation outside the radius of maximum wind (RMW) and the initial secondary circulation. With greater absolute angular momentum (AAM) beyond the RMW directly related to stronger primary circulation, and stronger radial inflow, Strong group is found to have larger AAM import in low-level, helping to spin up the TC. Initial moisture in inner-core is also critical to the intensity predictability through the development of inner-core convection. The aggregation and merger of convection, leading to the TC intensification, is influenced by both radial advection and gradient of system-scale vortex vorticity. Three sensitivity experiments are conducted to study the effect of model uncertainty in terms of model horizontal grid resolution on intensity forecast. The horizontal grid resolution greatly impacts the predictability of Lekima’s intensity, and the finer resolution is helpful to simulate the intensification and capture the observed peak value.