Temperatures in Christchurch have soared to a sizzling 30C as an early summer scorcher bears down on the country’s east coast.

The mercury hit 30.3C just after 1pm today in the Garden City. The North Island’s eastern regions are also tipped to reach highs around 30C today.

But the heat is not the only extreme factor today, with gusts of more than 100km/h recorded at the bottom of the country and a strong wind watch in place.

Gusts of 111km/h are being recorded on Stewart Island.

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 anticipated, with lows around 16C.

However, a cold southerly making its way up the country would mean a “dramatic” change in temperature looming.

“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,” MetService meteorologist Ngaire Wotherspoon said.

“Queenstown and Invercargill only got down to 16C last night, while their forecast low for tonight is 8C.”

Meanwhile, a strong wind watch is in place for Otago, Southland, southern and eastern Fiordland, and Stewart Island.

Gusts of 100km/h 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.