With that sort of slab going through it safely and effectively will be a major undertaking. It can be done but you would need to hire an engineer who specializes in such things ($), a contractor with experience is such things ($) who will use a lot of specialized equipment ($) to head off the cables and restore the integrity of the slab with a previously unplanned for hole in it. There is the construction motto: With enough time ($), materials ($), manpower ($), and money ($!$!$!)we can do anything.

Instead of all that how about a simple 6' or 8' square bump-out off the rear of the house. There are several small storm and tornado shelter designs that would fit in that footprint.

You would be building a free-standing storm room just a couple of inches off the back wall of your house. Ideally the design would be short enough to tuck underneath the roof overhang of the existing house as this would simply roof design. The gap between the existing house exterior and the shelter would be covered, inside and out, with a lightweight covering to keep the wind and rain out but designed to break away under if the house is swept away. Such shelters are required, for structural reasons, to be completely isolated from the house.

Typical shelter designs are typically 2x4s 16"OC with lots of connecting steel overlaid with double layers of 3/4" plywood and 18 ga galvanized steel sheet. Typical fastening of the exterior is 2" and 4" OC with 3" deck screws. Loads of screws. Those shelters are sometimes rated for an F-4 tornado (207 to 260 mph)and might give you some chance of surviving a F-5 (261 to 318 mph) as long as a windblown truck doesn't land on it. Once constructed the exterior of the shelter can be covered with material to match the exterior of the house.