In stark contrast with the North Island, temperatures in the South Island are soaring, with many areas surpassing 30C.

It comes as NIWA releases its seasonal climate outlook, and the heat is what many don't want to hear.

NIWA experts predict more heavy rain and possible flooding for the North Island in the coming months, with hot and dry conditions in the South Island.

High sea temperatures are likely to put autumn on hold.

"We could find summer lingering longer than what is typical because the ocean being warmer than what is usual delays that transition," NIWA's Chris Branolino explained.

It means hot days and nights are set to stay.

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"People think it's been a cool, bummer summer...But it's been muggy and really warm at night, so that translates to poor sleeping conditions," Branolino said.

As the City of Sails lingered about 20C today, Dunedin cracked 30C before midday.

Christchurch and Ashburton shared the top temperature at 33C, with hot days set to continue.

While NIWA said the current weather pattern is weakening, its impact will be seen for some time.