Humid weather is forecast to continue for the top of New Zealand on Monday, while there is also a risk of thunderstorms and tornadoes further down the country.
A low-pressure system over the Tasman is pushing moisture towards the upper North Island, causing the sticky air currently creating the balmy, island-like weather.
"This week a low pressure zone in the Tasman Sea is falling apart - but will take until Christmas Eve to do so," WeatherWatch says. "This system is very weak, but the moisture and instability it brings will be triggered by the summer heat and that means the risk for heavy downpours and thunderstorms."
"In the cool of the morning this moisture in the lower atmosphere may appear as drizzle, a brief shower, or simply dry with just some morning dew or clouds. The afternoon heat creates sea breezes which pushes inland and that pushes moisture and warm air higher up into the atmosphere and starts triggering isolated but big downpours and thunderstorms."
According to Weather.com, humidity in Auckland on Monday evening is expected to be at 82 percent, close to the level of humidity the website forecasts for Singapore. It will be slightly worse on Tuesday at 86 percent.
MetService meteorologist Dan Corrigan told RNZ the humidity will last through to Christmas, but won't be as bad as in recent days.
"It's just how Auckland is at this time of year. We see warm days and warm nights."
Metservice expects thunderstorm clouds to develop later in the afternoon.
"Over the North Island, the main risk of thunderstorms is about central and southern areas from inland eastern Bay of Plenty through the central high country to the Tararua ranges (including Gisborne/Hawke's Bay), and also inland Northland, this afternoon and evening."
In the south, there is a moderate risk of thunderstorms around northern and western areas from inland Tasman/Nelson and Marlborough to northern Fiordland and the Canterbury High Country.
These thunderstorms are forecast to be isolated and could produce heavy rain of 10-25mm/h and hail of 5-15mm in diameter.
"There is also a low risk of one or two very small and localised tornadoes or funnel clouds about the central North Island."
There's a low risk of thunderstorms for most of the rest of the North Island as well as western and inner parts of the South Island.
Whangarei is currently forecast to be the warmest part of the country on Monday at 25C, with Auckland, Hamilton, Tauranga, and Whanganui all expected to hit 24C.
Overnight Sunday, Whakatane was the warmest at 18.5C, while Gore was the coldest at 6.3C.
Short-term forecasts from Metservice:
Northland, Auckland, Waikato and Waitomo, also Coromandel
Fine spells and a few showers, some may be heavy this afternoon and evening, with possible thunderstorms about Northland.
The remainder of the North Island, also Marlborough and Nelson
Partly cloudy with scattered showers, some heavy with possible thunderstorms this afternoon and evening, especially inland.
Buller and Westland
Showers, some heavy and possibly thundery.
Canterbury
Mostly cloudy at first with areas of rain. Rain clearing by midday and fine breaks developing. However, isolated showers this afternoon and evening, some possibly heavy inland.
Otago, Southland and Fiordland
Some cloudy areas. Isolated showers, mainly from afternoon, then rain in the far south tonight.
Chatham Islands
Mostly cloudy. Occasional rain, clearing this evening.
