- Long-term mean rainfall rates from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR) are compared with in situ measurements by rain gauges on the NOAA TAO/TRITON buoy array in the tropical Pacific. The buoy rain gauges have an advantage over most of the available ground truth data in that they are not influenced by the local meteorological effects of islands. Instantaneous TRMM retrievals averaged over 1 x 1 longitude-latitude boxes are matched with 12-hour-averaged buoy rain amounts centered on the TRMM overpasses. The TMI has near-zero bias with respect to the gauges when compared across climatologically different gauge locations (dry to wet). The PR is biased about 30% low relative to the gauges. These results are consistent with other ground truth studies and the known biases between the TMI and PR in the TRMM version 5 algorithms. Because rain gauges are thought to underestimate rainfall during windy conditions, further study of gauge biases would be useful.