Maybe check your router firmware version and see if it needs to be updated, that seemed to fix my issue, but yours may not be the exact same issue.
or try right-clicking on the wifi icon at the top, chose turn off wifi, then chose turn on wifi. I've read that can fix minor connection problems when I was having the same issue.
Also if you haven't already, try unplugging the power to your router for a minute then plugging it back in.
Thats about all I can think of, I wouldn't take it to the Apple store until some more people reply here, maybe someone knows a fix.