Dunedin and Invercargill were 12C at lunchtime, but a puff of a northwesterly had brought a warm 19C to Christchurch, Coutts said.
Warm air from across the Tasman has moved on to eastern regions and is bringing an early taste of summer to parts of the country.
The warm spell is expected to last two days.
Niwa said the early-morning temperatures across the East Coast were more in tune with the average top temperature of an October afternoon.
Further south, heavy rain is affecting western areas of central and southern New Zealand.
MetService has issued a swathe of warnings and watches across the West Coast of the South Island and the Tararua Ranges and Mt Taranaki in the North Island.
More areas are likely to be placed on alert in coming days as stormy weather approaches New Zealand bringing windy and wet conditions to much of the country.
Heavy rain and thunderstorms are expected to cross Westland and Fiordland this evening.
A volatile combination of heavy rain and gales are expected to hit western parts of central New Zealand tomorrow.
MetService warns the rain is due to fall across the lower half of the North Island tomorrow night and gales will start late tonight at the top of the South Island before spreading across Cook Strait tomorrow morning and buffeting Wellington until late tomorrow night.
