Interaction of Tropical Convective Systems and Madden Julian Oscillation in Formation of Tropical Cyclone Mekkhala (2008)

Tropical cyclone (TC) formation close to Asian continent has significant impacts on coastal counties nearby. A case study of Tropical Strom Mekkhala (2008), which developed off the east of coast of Vietnam, is presented using the ECMWF YOTC high-resolution analyses and multiple satellite observations. A multi-scale view was explored as to how the initiation of the tropical cyclone occurred through interactions between Madden Julian Oscillation (MJO), Rossby-wave dispersion (RWD), and diurnally varying mesoscale convective systems (MCSs) upstream and over land. The YOTC analyses reveal the RWD from the pre-existing Typhoon Hagupit did a preliminary role in the formation. The RWD induces convective heating over the Philippine Sea, and the heating induced-vorticities were then merged into an organized but weak low-level vortex that arrived at Philippine. As Hapugit weakened due to landfall, however, the RWD effect did not finally lead to the formation. It was the MCSs associated with the MJO that contributed to the intensification the weak low-level vortex up to the TC intensity. At MJO phase 8, the strong westerly wind bursts were induced over the South China Sea that producing rich convections upstream and over the Philippines. In particular, a unique change in the diurnal variation of the convections was observed from the MTSAT-1R infrared images. That is, the MCSs enhanced off the west coast of the Philippines in the morning did not decay until evening, and merged with convective cells originated over the Philippines, which likely result in the initiation of the Mekkhala surface cyclonic circulation. Finally, the critical role of land-interacted mesoscale convective processes in TC formation near Asian continent is emphasized as well as the large-scale MJO and the synoptic-scale RWD influences.