Why… Front brakes squeak when applied lightly but not in a hard stop. Also, the squeaking does not start right away; it takes several stops. This was not noticed before this weekend (when temperatures exceeded 100°F).
You might be hearing the brake pad wear indicator rubbing the rotor.
Those are the metal tabs you see on the pads,
My 2016 EXL coupe V6 6spd does this too even though the brakes only have 20K miles on them with plenty of pad left.