The Nokia 8 naturally gets warm because it has a heat pipe on the CPU along with a aluminium body, so what you are feeling is the heat drawn away from the CPU and instead into the unibody so it can be dissipated, a good thing for performance!
If the ambient air temperature is very hot then yes it is normal, if the ambient air temperature is cool then no it is not normal.
How hot is it when you are seeing these temps on the phone?
Normal room temperature 22-25celsius. Just now cpu momentarily were 47-52 celsius and battery 39 celsius.
That doesn't strike me as particularly alarming if i am honest, when i was in Spain the other week my battery was regularly in the high 40's