The fine weather accompanying the first days of summer will remain for a couple of days yet, with temperatures expected to soar on Wednesday.

However "one of the larger storms of the year" is set to hit the country from Monday.

Napier overthrew Rarotonga as a sun seeker's dream on Sunday, reaching a scorching 28.8C at the airport, compared to Raro's 27.5.

Kaikoura was the hottest place in the South Island on Sunday, as the mercury soared to 28.6C. Hastings also tipped 28C, MetService meteorologist Tui McInnes said.

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Monday and Tuesday are expected to remain fine and sunny, but you may need to kick off those duvets at bedtime, with the heat sticking around on Monday night.

Aucklanders will slumber in a minimum of 18C, with 17C on the cards for Christchurch and 16C in Wellington.

But Monday evening will also see a large area of low pressure developing in the Southern Ocean, creating a large storm which will span thousands of kilometres and brush New Zealand and southeastern Australia.

WeatherWatch has described it as "one of the larger storms in New Zealand this year".

The West Coast will take the brunt of the heavy rain, with slips, flooding and road closures possible over the next seven days, WeatherWatch reported.

The wind will be fiercest in the Canterbury high country, and Wellington will have strong winds for much of the week, McInnes said.

A combination of wind and rain was likely to hit most of the country, McInnes said.

"Overall, you're more than likely to have some wet weather and some windy weather at some point," he said.

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Auckland will see a warm week, with the temperature reaching as high as 26C on Tuesday, with Christchurch faring the best out of three major cities weather-wise this week.

Mid-week is expected to be a high point for the temperatures, which will soar over 25C in Napier, Hastings, Timaru, Oamaru and Dunedin.

Dunedin's temperatures are expected to climb a few notches higher than this time last year.

Invercargill will also be warmer than usual, with temperatures expected to hit the near-to-mid-20s, McInnes said.