According to the United Nations Office for Disaster Risk Reduction, developing or least developed countries lack weather observation systems, making them more vulnerable to extreme weather events. Moreover, there is low sensor coverage and monitoring system sustainability in such countries. Also, using sophisticated meteorological equipment may not be scalable for these countries. Our research goal is to develop a warning system for localized heavy rains for developing or least developed countries by using a network of smartphones to facilitate current weather information. In this paper, we discuss the potential of smartphone-based measurements of radio signals, particularly of the 3G, 2.4 GHz, and 5 GHz WiFi, as a low-cost and scalable alternative for detecting localized heavy rains. As a result, we found that the trend in 5 GHz WiFi signal attenuation may best describe localized heavy rain events for detection and that it could be potentially related to humidity.