While it is true that daytime temps in Auckland are usually around 10C, it is also important to realize that the cold is often a damp cold. That can make it feel much chillier than the temp might indicate. Also, one of the biggest surprises I had coming to Auckland from the US was finding out that buildings do not have central heating. I had lived my whole life up to that point in the northern US and so was use to much colder temps, but still I found that many buildings here were colder than I had expected. I spent July and August last year in layers of clothing.