Extreme tropical humidity is yet to even peak in northern NZ, with Saturday looking to be the hottest, most tropical, day of this week.

As Cyclone Dovi unravels as it drops southwards it will drag down high humidity and heat from the tropics directly into the North Island.

WeatherWatch.co.nz says the South Island has a cooler air flow for the most part.

"Auckland has a high of 26 to 28 degrees on Saturday (hotter if the sun comes out) and coupled with very high humidity it may feel more like the mid to upper 30s if you're outside and moving around. You read that right," says a spokesperson for the weather organisation.

"But the overnight lows may be where people feel it the most. Auckland's overnight low on Saturday night will be 23 degrees, which exactly matches Nadi, Fiji on Saturday.

"Northern NZ literally will share the same air flow and temperature with very similar humidity levels too and for many it may feel more like 30C at midnight."

For those who are sick of the humidity, WeatherWatch.co.nz says there is a break coming.

"Auckland's overnight low is set to tumble six degrees by Monday night, and it's not just Auckland - most of the North Island will feel the cool down arriving on the back end of Dovi.

"The South Island isn't so impacted by the heat and humidity, although the next couple days and nights will be warmer. Christchurch was 17 degrees as daylight kicked in today while further north in the lower North Island Wellington was already at 22 degrees as the sun was coming up this morning.

"But that cooler change spreads from the south on Saturday and moves into the North Island over Sunday and Monday - depending on how the remnants of Dovi precisely travel."

This graph for Auckland - from RuralWeather.co.nz - shows how humidity (green shading and green arrow trend) reaches a peak on Saturday and Saturday night/Sunday morning... then eases into next week. Overnight lows will also drop several degrees.

Misery Index map shows how ex-tropical Cyclone Dovi will drag down tropical air which many will find "uncomfortable" on Saturday in the north - but note the cooler southerly flow in the South Island which heads northwards behind the remnants of Dovi.