The central objective of this study is to analyze the behaviour of GNSS products, namely Precipitable Water Vapor (𝑃𝑊𝑉) and Signal-to-Noise Ratio (𝑆𝑁𝑅), before, during, and after various intense rainfall periods to assess their precision and response time in detecting heavy rainfall. To achieve this goal, several GNSS stations are examined, covering Austria's entire territory within the EPOSA (Echtzeit Positioning Austria) area during the experimental period in July 2021. Subsequently, two different analyses are conducted, including (1) 𝑃𝑊𝑉 time series (sample rate 10 minutes) and (2) 𝑆𝑁𝑅 time series (sample rate 30 seconds), considering both lower and higher elevation angle ranges. These analyses are performed over multiple time windows to determine the response time of these parameters to heavy rainfall. As a result of this study, a new methodology based on 𝑃𝑊𝑉 and 𝑆𝑁𝑅 is investigated, demonstrating its potential for characterizing intense rainfall.