Three strong convective rainbands suddenly initiated and developed to the north of the landfalling typhoon Matmo (2014), where radar echoes were weak at the initial time. The intense convective precipitation later led to serious disasters over this region. The mechanisms for the convection triggering and developing processes are studied using the NCEP/NCAR final reanalysis data, automatic observation data and radar reflectivity data. Results show that the low-level frontal forcing combined with orographic lifting triggered the initial convection under the condition of symmetric instability and weak conditional convective instability. The rainbands were triggered by three convergence lines near the ground and kept developing when the convergence intensified under the circumstances of high humidity, persistent moisture convergence, and obvious convective instability accompanied with weak conditional symmetric instability. The forming positions of the three convergence lines are quite similar, which might be attributed to the difference in surface roughness between land and sea, the coastline curvature of northern Jiangsu and southern Shandong province, and the distribution of typhoon wind speed with radius. On the other hand, the generation of the second and third convergence lines was also closely related to the cold outflow from the previously formed convective rainband to its north. Strong precipitation centers along the convective rainbands often correspond to stable convergence centers that are located in the area with large wind velocity gradient. The wind speed gradient along the convergence line is mainly affected by the distribution of coastline, topography, and precipitation in the surrounding area.