It's possible that the change in weather has affected the tuning in the guitar. It is also possible that the strings weren't completely stretched out and/or are just in need of replacement.
Two things I would try if I were you:
1. Retune the guitar and play with it normally for a week and see if the problem goes away.
2. Inspect the guitar and see if the
neck screws are still tight, etc. Put a fresh set of strings on and see what happens.
Jimmy
