In reply to matus:
Sierra de Toix Toix TV area is a concave sun trap and can be very warm when other sectors are freezing.
Gandia (Penya Roja de Marxuquera) is also often very sunny, but it's worth checking the forecast local to Gandia before making the drive, as the weather than can be very different to that in Altea.
Hope you have a lovely holiday, and if you're there for New Year's Eve don't miss the Three Kings parade in Calpe!
Post edited at 11:04