Wellington, or Te Whanganui-a-Tara as it's known in Maori, is beautiful no matter what time of the year or season you visit. So the best time to visit is pretty much the time that suits you best. However, if you have more than one date in mind, the following information may help with your travel plans.
The warmest months of the year are from September through April; being Downunder, this is spring to the end of summer. December, January and February are the three hottest months of the year (summer). Spring is from September through November. Autumn (or fall) is from March through May and the winter season runs from June through August. Maximum daytime temperatures vary from 15 to 30+ degrees (Celsius) in the summer, 10 to 25 degrees in the autumn (and spring) and 5 to 18 degrees in the winter.
Before you arrive, and while you're here, weather forecasts and historical weather pattern information can be obtained from the Metservice website (www.metservice.com).