There was a huge debate on this board a few years ago about this very topic. I'm pretty sure SpiffyKyle was involved.

If I remember the gist of his argument, he stated that humidity is directly affected by temperature. So, in other words, the lower the temperature, the harder it is to achieve optimal humidity. Is 63 degrees too cold? Probably not, but 53 might be. I don't know. At any rate, I'd make sure my hygrometers were properly calibrated and check them often.