Causes of heavy rainfall during the meteorological safeguard period of 2023 Boao Forum

In the report， the conventional observation， radar， and ERA5 reanalysis data were used to analyze the causes of the heavy precipitation during the meteorological safeguard period of 2023 Boao Forum in Hainan Island. The results indicated that the convergence of the water vapor flux is mainly concentrated in the near surface layer. The easterly wind in the near surface layer is almost perpendicular to the terrain in the eastern part of Hainan Island， and the favorable terrain uplift triggers convection. The cyclonic flow generated by the terrain is conducive to the development of convection. The unstable convective stratification and vertical shear of environmental wind affect the development， the maintenance， the movement， and the propagation of the convective system. Comparing the difference of the precipitation in the morning of the 29^th， the 28^th， and the 30^th under the similar circulation background， the atmospheric uplift condensation height （LCL， 121.4m）and the level of free convection （LFC，636.6 m）on the 29^th are lower， the thickness of warm clouds is larger， and the wind direction near the ground is close to the easterly wind， which is more conducive to the precipitation in the eastern.