Cloud evolution during tropical cyclogenesis was examined using the TRMM PR products from 3 days before to 1 day after genesis. Precipitation increases substantially within 36 h before genesis. Stratiform clouds, mid-level convection, and deep convection all contribute to the increasing precipitation. The contribution by stratiform precipitation is due to its increasing areal coverage, while its pixel rain rate changes little from Day -3 to Day +1. The contribution by mid-level and deep convections results from their increasing areal coverage and intensifying rain rates. Among the three types of convection, deep convection has the largest pixel rain rate, but mid-level convection occurs most frequently and makes the largest contribution to the total precipitation. The overall contribution by convective clouds, despite their low areal coverage, is comparable to that by stratiform precipitation. It is suggested that tropical cyclogenesis may be an outcome of the collective contribution by different precipitation types.