The prediction and understanding of rapid intensification (RI) of tropical cyclones (TCs) has always been a challenge. The maximum wind speed (V_max) and the minimum central pressure (P_min) are two commonly used TC intensity indicators. In most existing works, they only choose a single indicator (mostly V_max) to investigate the RI process. Whether there is a difference between the RI defined by 24-hour changes of V_max and 24-hour changes of P_min, and what the relationship between RI in V_max and RI in P_min are the issues that deserve to be discussed. The study found that rapid changes in V_max and in P_min are not always accompanied. RI cases can be divided into three categories: 1) both the V_max and the P_min experienced rapid change (RI_pv), 2) only Vmax strengthened rapidly (RI_v), 3) only P_min decreased rapidly (RI_p). Each type of RI exhibits distinctive TC structures and convective features. At the onset of RI_v, the TC intensity is weakest and the TC fullness is smallest. The deep convection is concentrated in the inner-core region. For RI_p, the TC intensity is strongest and the TC fullness is the largest. P_min, as an integral variable, reflects not only the TC intensity but also the TC size. For the cases that only rapid change in V_max (RI_v), the TC size expands slowly. For the cases that only P_min deepens rapidly (RI_p), the outer circulation enhancement is most evident. Thus, RI classified via these two commonly used TC intensity indexes (V_max and P_min) could help us further understand the relationship between TC size and TC intensity.
 

Tropical cyclone; Rapid intensification