Check out the 15 day weather forecast via the link below. It does forecast thunderstorms for Friday, and possibly Saturday, but from then on you will see a vast improvement. Lots of Sun, High Temps, etc.
Rain and Thunderstorms are normally short lived anyway.
Regardless of the weather, enjoy yourself in Corfu, Happy Holidays.
PS: I will add that no weather forecast is accurate, as I have just looked at others and they forecast sunny and hot weather. Make your own mind up,