What would cause a grinding noise every time the steering wheel is turned either left or right - worse in warm weather?

Check the fluid. If it is full, the pump is worn and eventually will fail but it may last a good while longer. Check the fluid level first though.

answer sounds like wheel bearings are wearing out, or the steering column bearings inside the steering colum

If the vehicle is front wheel drive then you may also need to check the right and left side CV joints on the drive shafts..many times the rubber boots covering these joints degrade and crack allowing dirt/moisture to enter the joint and allow the grease to exit,this will cause a grinding noise when turning..If left unchecked the joints will fail and the car becomes undrivable...

There are 2 CV joints on each drive shaft one right behind wheel housing(hub) and one next to the transmission...

CV= (constant velocity)