In this study,to explore the strength and structure of sea breeze under cloudy conditions over Hainan Island,the 3D high-resolution numerical simulation of sea breeze on July 5,2012 was conducted by means of non-hydrostatic mesoscale model WRF,coupled with the Noah land-surface model.Hainan Island is a tropical island with oval topography.The frequency of occurrence of sea breeze is high throughout the island,due to its geographical location and unique topography.In addition,cloudy skies under weak stable weather conditions are conducive to the triggering of sea breeze,according to previous researches regarding the statistical analysis of sea breeze over Hainan Island.Therefore,it is significant to study the structure of sea breeze circulation on July 5,2012,when the sea breeze observed was conspicuous,and there was a large number of clouds over the island during the evolution of the sea breeze.Compared with the observational data,the results show that the evolution and characteristics of sea breeze can be reasonably simulated by WRF.The evolution of sea breeze under cloudy conditions resembles sea breeze under clear conditions.Formed at 12:00 BST throughout the whole island,sea breeze circulation was strong during the time range of 15:00-18:00 BST in flat areas,and strong during 13:00-18:00 BST in mountainous areas.A significant convergence line was finally observed on the island at 18:00 BST.Strong convective weather could be easily triggered under the convergence of sea breezes for the deep convective instability energy and abundant water vapor,i.e.the convergence zone of sea breezes is the main potential precipitation area.The complex terrain has direct and indirect effects on the structure of sea breeze circulation.It determines the distribution of the low-level horizontal wind field,then affects the characteristics of sea breeze in all directions indirectly.The sea breeze circulation becomes clear,the sea breeze front is almost perpendicular to the ground and its strength enhances,then the sea breeze convection can last for a longer time,indirectly due to the blocking and lifting effect of the mountain.At the same time,the valley breeze circulation forms and disappears almost simultaneously along with the sea breeze.Therefore,the valley breeze circulation interacts with the sea breeze circulation on the same side of the mountain.On one hand,this can cause frontolysis of the sea breeze front when the valley breeze strengthens suddenly,otherwise it causes frontogenesis of the sea breeze when the valley breeze weakens.On the other hand,the circulation becomes more pronounced and strengthened when the valley breeze overlaps with the sea breeze.However,in flat areas,the dynamic and thermal effects of the terrain are weak.The sea breeze pattern in flat areas is more regular than in mountain areas.Sea breezes from different directions gather together,and some convective clouds merge in the convergence of sea breezes.Furthermore,the variation of sea breeze circulation mainly depends on the interaction with sea breezes from different directions.