Weather in La Coruña is always changing, from one day to another, from one hour to another. You can start with sunshine and have rain in a few hours. From May till September temperatures are usually best for the visitor. Winter is usually cold and rainy. However expect the odd day where you can find temps in the high-teens centigrade.

June,  July and August are the real summer months here. This does not mean it wont rain, but temperatures are on the whole great. Not too hot, not cold. That means that there are some Spanish tourists (mostly from Madrid). Foreigners have  yet to discover La Coruña.

For someone looking for the great beaches July and August would be the time. For someone looking for the rest (food and nature) It is  recommended that they visit during September. Nice weather, no tourists.