The South Island and central North Island are set to have a reprieve from the hot and muggy nights, and there is even a chance of snow in Fiordland.

The National Institute of Water and Atmospheric Research (NIWA) said minimum temperatures in the South Island and central North Island would almost exclusively be below 10 degrees Celsius overnight.

"Temperatures tonight are set to plummet in many areas, with Alexandra forecast to drop to 3°C, and Queenstown and Wanaka to 4°C. Hastings will see a drop of 20°C, from 32°C to just 12°C tonight," said MetService Meteorologist Dom Barry.

There was also a "possibility of snow flurries" about the Fiordland Ranges to 800m this afternoon.

"The change to cooler air also brings the possibility of a light dusting of some unseasonable snow falling about the very highest parts of Fiordland, Southland, Southern Otago, and the Canterbury High Country. However, with the recent warm weather we have had heating the ground, it is unlikely any snow will settle," Barry said.

Wednesday was set to be mainly fine, with showers in the eastern coasts. A period of settled weather for most was expected on Thursday.

Heading into the weekend, temperatures are once again set to rise into the mid-to late 20s for most. Then on Friday some possibly heavy rain for Fiordland and Westland.

Meanwhile, MetService was monitoring a tropical cyclone brewing off the coast of Australia, but it was not yet clear if it would boomerang back to New Zealand.

"The current forecast is for this system to move westwards towards Australia and Queensland on Thursday," it said in a statement.

Main image (RNZ file image 123rf): Summer snow flurries are expected in Milford Sound today.