On Tropical Cyclone Genesis Types and Their Intensification Rate

Higher tropical cyclone (TC) intensification rates are associated with a smaller radius of maximum wind (RMW). Previous studies have shown that convection distribution is affected by the TC genesis type. However, no studies have identified the impacts of TC genesis types on both the initial RMW and convection distribution. In this study, a new objective method is developed to classify TC genesis types based on the K-means clustering algorithm of critical atmospheric parameters available from reanalysis data. For comparison between intensification rate and RMW, the lifetime maximum intensification rate (LMIR) in each case is also examined. The result shows an inverse relationship between the LMIR and the RMW during the LMIR period. Furthermore, TCs with larger initial RMW usually have lower LMIR, implying the importance of initial RMW. The K-means cluster analysis shows four TC genesis types: (i) easterly wave (EW), (ii) monsoon confluence (MC), (iii) monsoon shear (MS), and (iv) monsoon depression (MD). EW has the most aggregated convection and a moist area only around the center, explaining why the EW type has a small RMW. In contrast, MD has more scattered convection and larger circulation than others. Consequently, MD has a significantly larger initial RMW and lower LMIR than EW. Although both MC and MS have medium RMW sizes that fall between those of EW and MD, their LMIR is as high as that in EW because of aggregated convection similar to EW, resulting in RMW contraction and an LMIR similar to EW.