It's been a bit cooler northwards, with balmy temperatures around 18C in Wellington and Auckland paired with a light breeze.
November owes its warm welcome to a warm mass, courtesy of Australia, channelled over New Zealand by a big high pressure system parked over the Tasman Sea. James said current temperatures are well above normal for this early in November.
"A lot of them are 6 or 8 degrees above the long term average in November," he said.
"To see temperatures this warm this early in spring is unusual."
New Zealand's hottest November temperature on record occurred at Lake Coleridge (35.6C, 1920) followed by Gisborne (34.8C, 2016).
Niwa reported several spots in inland Otago might have hit record figures even yesterday - they included Clyde (32.5C), Alexandra (32.2C) and Windsor (30.8C).
But today is set to be the warmest day, with temperatures beginning to fall next week.
READ MORE:
• Weather: Hot temperatures and a fine weekend ahead for many
• Labour weekend weather: Hot days ahead for some, wet for others
• Weather: Mainly fine for the North Island ahead of soaring temperatures nationwide this weekend
• Weather causing chaos in Christchurch
James said the weather will stay "pretty warm" over the next few days, before a front moving over the South Island on Wednesday will start to drag temperatures down.
It's also looking a little cooler in the North Island towards the end of next week.
Later, during the second week of November and into the middle of the month, some strong fronts were possible in the South Island, bringing rounds of heavy rain and an increased risk for areas of flooding, especially in the west.
MetService predicted that, overall, monthly temperatures for November would end up above average for northern and eastern regions of both Islands, with prevailing mild northwesterly winds and near-normal rainfall for most places.