In this paper we detail our processing system for blending total precipitable water (TPW) data from the Advanced Microwave Sounding Unit (AMSU) instruments on three NOAA satellites with data from the Special Sensor Microwave/Imager (SSM/I) instruments on three Defense Meteorological Satellite Program (DMSP) satellites to form a unified product. The discussion includes grid computing techniques and dynamic cross-sensor intercalibration. Nearly global, Mercator TPW composites are constructed hourly and made available in real time to forecasters.