Highs of 28C, 31C and 29C were forecast for Napier, Hastings and Gisborne while other northern centres could expect temperatures in the mid-20s.
Overnight temperatures were also expected to be above normal. In many regions, such as Auckland, warm and humid nights are expected, with lows around 16C.
Wotherspoon said southern areas of the country were also expected to reach the high 20s. Timaru was expected to reach 29C and Christchurch 28C.
However, a cold southerly making its way up the country would mean a “dramatic” change in temperature.
“Queenstown and Invercargill only got down to 16C last night, while their forecast low for tonight is 8C,” Wotherspoon said.
Meanwhile, a strong wind watch is in place for Otago, Southland, southern and eastern Fiordland, and Stewart Island.
“There’s a cold southerly change moving up the South Island this afternoon and evening, weakening as it progresses, and northwesterly winds are strengthening ahead of the change,” Wotherspoon said.
100km/h gusts have already been recorded on Stewart Island this morning and winds of the same strength are expected throughout the day in exposed places.
A strong wind watch has also been issued for Wairarapa and Hawke’s Bay.
A heavy rain watch is in place for Fiordland.
With a high of 17C predicted for Christchurch, tomorrow will be much colder for the South Island and cooler for the North Island as the southerly trend continues northward. Temperatures are expected to peak in Kerikeri and Tauranga with highs of 26C.
Niwa reports temperatures are likely to be warmer than average through to January, with frequent northwesterly winds leading to more days above 25C.
Also raising the odds for hot summer weather was the potential for marine heatwave conditions – already occurring in seas to the east of New Zealand – to expand and intensify.
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