Weather patterns are strongly affected by the prevailing westerlies, which suck up moisture from the Tasman Sea and dump it on the western side of both islands. The South Island gets the lion's share, with the West Coast and Fiordland ranking among the world's wettest places. The mountain ranges running the length of both islands cast long rain shadows over the eastern lands, making them considerably drier, though the south is a few degrees cooler than elsewhere, and sub-tropical Auckland and Northland are appreciably more humid. In the North Island, warm, damp summers fade almost imperceptibly into cool, wet winters, but the further south you go the more the year divides into four distinct seasons.

Such regional variation makes it viable to visit at any time of year, provided you pick your destinations. The summer months are the most popular and you'll find everything open, though often packed with holidaying Kiwis from Christmas to the end of January. Accommodation at this time is at a premium. In general, you're better off joining the bulk of foreign visitors during the shoulder seasons - October to Christmas and February to April or May - when sights and attractions can be a shade quieter, and rooms easier to come by. Winter (June-Sept) is the wettest, coldest and consequently least popular time, though Northland can still be relatively balmy. The switch to prevailing southerly winds tends to bring periods of crisp, dry and cloudless weather to the West Coast and heavy snowfalls to the fine, under-utilized and plentiful skiing pistes of the Southern Alps and Central North Island.