if you go to http://www.wunderground.com/global/stations/16716.html?bannertypeclick=bigwx

put in the nearest airport and using all the keys you can find the History of the weather for that area over recent years for your holiday period.. note these are past weather and no one can grantee whats likely to happen this year

wizard

The weather in October can be a bit hit & miss. Some sun, some rain. You could get lucky and have decent weather all the time.
A few years ago we went Halkadki, which is further north than Zante, and we had great weather all week.
I'm almost certain they'll be more sunny days than rainy days.
Have a good time!