Bay of Islands in August

October through April is peak season, and for good reason — the water temperature hits 22°C, perfect for swimming and water sports. December and January bring the crowds and the highest accommodation prices, but also the warmest weather and longest days. I prefer visiting in March or April. You get the warm water and sunny days without the Christmas holiday madness, plus accommodation prices drop by about 30%. The shoulder months of October and November can be brilliant — fewer crowds, good weather, and the pohutukawa trees start blooming their famous red flowers. Winter (May to September) sees temperatures drop to around 15°C, but it's still pleasant for hiking and exploring historic sites. Just don't expect to swim much, and some tour operators reduce their schedules. Rain can hit any time of year, but winter tends to be wetter with more persistent drizzle.