New Zealand is in for a fine weather treat as the world's "strongest high pressure" weather system drifts over the country.

"Guess what? The world's strongest high pressure system is set to move over New Zealand later this week," Niwa says in a tweet.

It said the air pressure could go as high as 1040 Hectopascals (hPa).

Niwa forecaster Ben Noll said although not unprecedented, hitting that level of air pressure will make a meteorologist "sit up and take notice".

Atmospheric pressure is the force of air pulled towards the earth by gravity. The highest pressure recorded in New Zealand was in Wellington in 1889 at 1046 hPa.

"What this high pressure will bring is fine weather, clear skies and light winds and for some, frosty mornings," Noll said.

WeatherWatch is forecasting a mix of sun and cloud for most of upper North Island regions tomorrow and a mostly sunny day for the lower North Island.

It will also be mostly sunny for the east and north of the South Island.

Moving into the weekend, it would be mainly fine for most of the country on Friday and Saturday.

The Central Plateau, Wairarapa, inland Marlborough and Otago can expect a frosty morning on Friday, following clear overnight skies.

Isolated showers are possible from the afternoon for eastern parts of the North Island on Friday, and patchy rain or drizzle from Saturday afternoon in Fiordland and southern Westland.