The purpose of this paper is to retrieve the oceanic rain rate (RR) over waters near Taiwan and Luzon from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) multi-channel brightness temperatures (Tbs). In addition to improving heavy rainfall forecasting by providing quantitative oceanic RR estimates and possible movement direction of Mesoscale Convective Systems (MCSs), another objective of this paper is to overcome the lack of oceanic conventional observations in heavy rainfall forecasting during the Mei-Yu season. Rainfall caused by MCSs during the 1998 South China Sea Monsoon Season. Rainfall caused by MCSs during the 1998 South China Sea Monsoon Experiment (SCSMEX) was studied using TMI nine-channel Tbs, the hourly RR from ground rain gauges, and Geostationary Meteorological Satellite (GMS) infrared (IR) Tbs. In this paper, the domain rages from 110°E to 130°E and from 15°N to 30°N. Two oceanic RR retrievals taken on 3 June 1998 are shown and examined. The results show that a TMI nine-channel Tbs-RR equation can retrieve the amounts of heavy rainfall caused by the MCSs that often occur during the amounts of heavy rainfall caused by the MCSs that often occur during the summer monsoon season in southeastern China, the northern part of the South China Sea, Luzon, and southern Taiwan. The RR retrievals were quantitatively consistent with the rainfall observations made on nearby islands. The GMS IR Tb 240K isotherms included most of the TMI microwave (MW) Tbs retrieved rainfall region. The heaviest rainfall region was more or less included in the area where the IR Tb was colder than 210K. The region had a tendency to be concentrated in the forward part of the MCS in the direction of its movement. Morever, analyses of the rainfall events that occurred in Southern Taiwan during the SCSMEX period show that there was local rainfall enhancement caused by the orographic features of the island.