Recently, continuous outbreaks of the white-backed planthopper (WBPH) Sogatella furcifera (Horváth) have caused heavy rice yield losses in China. Hunan Province is a hotspot in principal migration pathways, and consequently, the main infestation area for the rice planthopper species; therefore, significant economic damage caused by WBPH outbreaks in this province will directly threaten food security in China. Therefore, a better understanding of the source areas and landing mechanisms of immigrant planthoppers in a mesoscale region such as Hunan Province would be essential for an accurate and detailed offsite forecast based on the hopper occurrence status in the source area. A trajectory analysis method based on atmospheric conditions has been developed for the quantitative simulation of population movements and distributions over a range of temporal and spatial scales. Meanwhile, the Weather Research and Forecasting (WRF) model can not only improve the precision and accuracy of trajectory calculation by providing a meteorological background with high spatial and temporal resolution, but also describe and interpret the WBPH migratory mesoscale process by analyzing atmospheric parameters with its advanced numerical technique. In this study, weather datasets on peak days of light-trap catches of the early immigrant WBPHs in Hunan Province during late April and early May of 2012 were selected to conduct a three-dimensional trajectory analysis and a multifactor spatio-temporal dynamic analysis to simulate the migration processes with the WRF model. The following results were derived from the analysis: (1) From April to May 2012, immigrant populations of WBPH in western Hunan were mainly from northern Vietnam and southwestern Guangxi and partly from southeastern Guangxi and southern Guangdong. Source areas of WBPHs that immigrated to southeastern or central Hunan were traced back to southeastern Guangxi and southern Guangdong and partly to Hainan. In late April and early May, source areas of migrant WBPHs were relatively different between western and eastern Hunan. A prevailing southwest monsoon and obstruction by the Nanling Mountains ensured that fewer early immigrant WBPHs landed in southeastern Hunan than in southwestern Hunan. (2) The source populations of WBPH were carried by the southwest low level jet and then clustered and forced to land by downdrafts, a low temperature barrier, and precipitation, which was caused by a frontal cyclone, shear line, or strong updraft, with the application of a three-dimensional trajectory analysis and meteorological modeling. (3) The landing areas of the early immigrant WBPHs were primarily along the Wuling mountainous region in western Hunan, the Xuefeng mountainous region in southern Hunan, and the eastern end of the Xiang-Gui Corridor. Terrain-forced flows (winds modified or channeled by the underlying complex terrain) are associated with mountainous terrain. Thus, terrain was believed to be a main factor that forced massive numbers of WBPHs to land and immigrate frequently into western Hunan. Most of the immigration events and insect convergence occurred in valleys and on the windward side of mountains owing to the vortex effect caused by mountain blocking and friction, mountain breezes, and ravine winds in a valley.