That's nothing to worry about.
These tires were made that way, so as they wear in, you get better dry traction.
The grooves you're concerned about when new, are not even 1/8" in depth.
What you want to look for are the "wear indicators".
When the tread is to that depth is when they need to be replaced.
I got this pic from someone else, but check the red arrows.
Those are of the wear indicators.
You'll find them in several different places around the circumference of the tire.
Sometimes, there will be a little triangle on the sidewall to tell you where they are.
You have been rotating them.....haven't you?
I do mine every oil change.
In fact, here's a related thread with some more pics.
Happy reading.....check about 1/2 way through the thread where I discuss it.