Secondary eyewalls (SEs) are very common in intense tropical cyclones. The storms usually experience dramatic changes in both intensity and structure after the SE formation. However, the sizes of SEs and associated intensity change can vary in cases. Numerical sensitivity experiments and observational studies are conducted to investigate the possible mechanisms from both internal thermodynamics/dynamics and large-scale environment on secondary eyewall replacement cycles.
I will also present some recent works on the dynamics and predictability of tropical cyclone formation and track will be introduced. Using ensemble forecasts from both the mesoscale regional model and global model, we examined study factors affecting the genesis of Hurricane Karl (2010) and the sudden track change of Typhoon Megi (2010) based on the discrepancies between ensemble members.