Climate of Cadiz is mild Mediterranean type. It has warm, dry summers and mildly cool winters. Average annual temperature of Cadiz is around 18 degree Celsius.
Summer: The hottest months are July and August and the wettest months are September and October. If you enjoy extremely hot weather, the best months to visit Cadiz are between the middle of May and end of September which is considered as good season for visitors. The negative side to this are the massive crowds of tourists.
Winter (November - January): Winters are mild in Cadiz and the best time to visit this place. The visitors can enjoy outdoor activities and relish the cool weather.
Monsoon: The wettest months are September and October. These months are probably off season in Cadiz. Avoid planning your Cadiz tour then.
So, the best time to visit Cadiz is from October to January.