The United Nations Early Warning for All program was launched, because flood early warning is seen as one of the most effective ways to reduce the impact of flooding. The development of flood early warning systems in urban areas is challenging. This holds everywhere, but even more so in the rapidly growing cities of large parts of Africa. This is due to a combination of the severity of local storms in the African climates and the lack of adequate observations and forecasts, which highly reduces the anticipation options for urban flooding. In this project, we demonstrate the development of an urban flood warning system, which leverages globally available data and openly available modeling setups. This makes the approach applicable for other cities in Africa as well. The integration of the urban flood warning system in the impact-based forecasting platform of Red Cross and the East Africa Hazard Watch ensures that warnings are effective and that pro-active action by local stakeholders and the humanitarian aid sector is made possible.