One of the most neglected aspects in home maintenance is that of window maintenance. Wood windows do have the propensity to swell when exposed to damp and wet. This can be solved through regular maintenance.
Wait For Dry Weather
The best way to deal with wooden windows is to wait until the weather is completely dry. This would allow for the swelling to stop and for it to shrink down. This step is important because you will end up sanding away too much and end up with a window which does not seal well. Only then can you have a look at how much work you need to do in order for the window to be repaired.
Scrape, Sand, and Refinish
Once you have established how much actual swelling there is, you can start by scraping off all old paint or varnish. Once that is done, sand the wood starting with a coarse grade. You should also give it a final sanding to prepare the surface with a finer grade sanding paper. Replace any missing glazing with insulating putty. Finally, paint several layers with good wood paint or varnish.