We discuss the basis of a regional-scale operational flash flood guidance diagnostic system. In this context, flash flood guidance is the volume of rainfall of a given duration that is enough to cause minor flooding in small catchments. The Central America Flash Flood Guidance (CAFFG) system, apparently the first of its kind, was recently implemented in San Jose, Costa Rica, and it provides 6-hourly flash flood guidance estimates for the seven countries of Central America with an average resolution of 200 square kilometers. These estimates are transmitted in real time to all seven countries of Central America for use by the National Meteorological and Hydrological Services for the development of forecasts and warnings. This GIS-based system contains components for ingesting and processing real-time geostationary satellite precipitation estimates, real-time hydrometeorological data from data collection platforms (DCP) located in various countries of Central America, and real-time World Meteorological Organization (WMO) data available on the internet. This talk focuses on the system design and implementation as well as on system testing, operation and internet-based product development. We suggest that the state of development is such that it is now possible to implement this system globally to allow early flash-flood warnings in flash flood prone areas around the globe with high spatial resolution.