Martens said that mean fog, or 100 per cent humidity was likely this morning.
"That is unheard of. It is what you expect in the Cook Islands and the tropics."
A westerly change will bring dry air and a pleasant high for Thursday and Friday but the humidity returns as Tropical Cyclone Gita enters the Tasman Sea.
The category 4 cyclone passed just below Tonga overnight, hitting the nation with winds of 195km/h and 150-250mm of rain.
It is now moving towards the southern islands of Fiji and is likely to become a category 5 cyclone today.
Tropical Cyclone Gita is scheduled to pass south of New Caledonia on Saturday before travelling south into the Tasman Sea.
"Early next week there is a chance it may reach New Zealand, but the model is still uncertain," Martens said.
"Once it moves out of the tropics and the sea temperature decreases it will lose a lot of its power.
"Even if it gets up to a category 5 it will likely be a 3 or a mid-level 2 storm if it reaches here."
Today's weather
Northland, Auckland, Waikato and Bay of Plenty:
Areas of rain, chance of heavy falls / thunderstorms otherwise fairly patchy. Humid north to northeasterly winds continue.
Highs: 25C-26C
Western North Island (including Central North Island):
Cloudy areas, may be a shower or two more so in the afternoon. Becoming drier again in the evening. West to northwesterly winds.
Highs: 23C-26C
Eastern North Island: Areas of rain, more so about Hawke's Bay where there could be heavy falls and even a thunderstorm or two. Gisborne and further south about the Wairarapa may be fairly dry with high cloud although a shower or two in the afternoon can't be discounted. Winds from the northerly quarter.
Highs: 25C-29C
Wellington:
Sunny spells with north to northwesterly winds, easing from afternoon.
High: 23C
Marlborough and Nelson:
Sunny, some cloud develops overnight. Afternoon northwesterlies for Marlborough, afternoon northerlies for Nelson.
Highs: 26C-30C
Canterbury:
Sunny weather with afternoon east to northeasterly winds, some cloud moves in later in the evening or overnight.
Highs: 24C-27C
West Coast:
Morning cloud with a drizzle patch or two then sunny areas increase from afternoon, light winds tend southwest after midday.
Highs: 22C-27C
Southland and Otago:
A few showers pass through Southland late morning then into
Otago
(especially in the east) late afternoon / evening. Showers about eastern Otago may be heavy then clearing at night. Before showers move in conditions are mostly sunny with northwesterlies, changing south to southwest as showers move in.
Highs: 18C-27C
Source: Weatherwatch NZ
