A TRMM-based 3-hr analyses that uses TRMM observations to calibrate polar-orbit microwave observations from SSM/I (and other satellites, including AMSR on AQUA and ADEOS II) and geosynchronous IR observations is described. The various calibrated observations are combined into a final, 3-hr resolution map. This TRMM standard product will be available for the entire TRMM period (January 1998-present) in 2003 as product 3B-42 of the TRMM Version 6. A real-time version of this merged product is being produced and is available on the U.S. TRMM web site (trmm.gsfc.nasa.gov) at 0.25∞ latitude-longitude resolution over the latitude range from 50N-50S. Validation results indicate that useful daily rainfall estimates are being made, although the real-time product has a positive bias over mid-latitude land areas in summer. Application of these real-time estimates in monitoring floods is explored using case studies in the U.S. (for validation) and in many locations worldwide. Numerous heavy rain events are detected, both small, localized cases and those resulting from larger-scale events. Limitations due to orographic processes are examined.