1. The sentence indicates that the individuals were already in a basement shelter when they heard the tornado approaching. This suggests that they had taken safety precautions and sought shelter before the tornado arrived.
2. The use of the word "approaching" indicates that the tornado was getting closer to their location. The sound of a tornado can vary, but it is often described as a loud, continuous roar similar to a freight train.
3. The ability to hear the tornado approaching from the basement shelter highlights the importance of being alert and aware of severe weather conditions. Being able to hear the tornado allowed the individuals to stay informed about the tornado's proximity and take necessary precautions to stay safe.
