Storms do not differentiate what part of your house they will affect.
When a storm move through and overload local sewer systems with water run off. This water is pushed through into the path of least resistance.
All too often this means through bathrooms and into homes from sinks, toilets, bath tubs and showers.
When that happens there is not much you can do until the issue is stopped outside. Resulting in a large amount of damage throughout your home.
Please know this back up is not clean water. It is very contaminated and has a lot of potential for bacteria, virus and fungus.
Make sure you keep out of the area until professionals are able to get in and clean it up.