When it is hot out (above 75 degrees air temp) and only when the air temperature is hot and nothing to do with the car being driven for a while or anything, the brake pressure gets really weak and I can almost put the pedal to the floor with greatly deminished braking ability. If I release the brake it will “refresh” and I can get a little more braking ability before I have to repeat the process. Why on earth does this happen? Again, it ONLY happens when it is really warm outside.
Is there any brake fluid leaking? Check behind the tires.
Is the reservoir fluid level up to the recommended full mark?
If no to both the above, then you MAY have a faulty master cylinder or booster.
Sounds like your brake master cylinder is getting ready to fail. Get it checked ASAP. Rocketman
When this happens, pop the hood and run water at low pressure from your garden hose over the master cylinder (the body of the unit, not the brake fluid reservoir); if that fixes the problem, and I think it will, you need a new master cylinder. Good luck.