This isn't just summer: meteorologists say the heatwave currently engulfing the country is an abnormal event. Science reporter Jamie Morton tackled the five obvious questions surrounding it.

Where did it come from?

The warm blob of air presently parked over the country has been tied to a big dry that's hit Australia and left dozens of horses dead.

Some have pointed to meteorological influences that heated things up further in Australia, resulting in a full-blown heatwave in parts of the continent which then flowed out into the Tasman Sea.

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But MetService meteorologist Dr Georgina Griffiths said that warm slab of atmosphere would have made its way here to New Zealand, regardless of what played out across the ditch.

"It's obviously been helped along a little by the fact they've had some dryness over there, but even if Australia was absent, and it was just sea, that warm blob would have come through."

When it did arrive over New Zealand, it mixed with our thicker, heat-trapping atmosphere – and amid a prevailing high pressure system that had already settled local weather conditions.

Why are some places feeling it much more than others?

As always, New Zealand's maritime geography was the general factor at play here.

Griffiths said the slab was blanketing nearly all of the country, but some spots had felt the heat more keenly because they hadn't been sheltered by cooling sea breezes.

"Places like Taranaki and the west coast of the North Island have gotten some of that cooler maritime air, whereas if you look at anywhere down from Bay of Plenty, through Gisborne, Napier and Masterton, they all hit around 33 or more yesterday as they didn't get those cool sea breezes."

Auckland was also relatively sheltered by a breezy day yesterday but that certainly wasn't the case today, with temperatures expected to reach a high of 30 in central parts of the city.

"While north of Whangaparoa gets an easterly later today, and it gets a bit cooler as you go further north," she said.

"So, basically, our subtleties in wind flow and in coastal breezes make a big difference."

Our oceans have been warmer at the moment. Does that have anything to do with it?

Over past weeks, sea surface temperatures surrounding New Zealand had climbed to more than 1C above the long-term average.

Waters had warmed particularly around the South Island and to the west, south and east of the country – and scientists had been closely observing whether another marine heatwave would unfold.

But Griffiths said a front that had just passed through had knocked down much of the heat on the ocean surface.

"We still do get a little bit of modification, because we the combination of light winds and a warmer sea will equate to warmer air temperatures for coastal areas.

"But the recent wind we've seen has cooled things off dramatically along the west coast of both islands.

"So while it's still warm over the Tasman Sea and warm over our eastern coastline, and that plays a part, the mechanism for the warmth we are feeling now is still that slab of atmosphere."

How long is it here for?

Meteorologists haven't been calling this system a heatwave for nothing.

After all, a heatwave is when the daily maximum temperature is higher than the average maximum by at least 5C for five consecutive days – and that's what we are seeing this week.

But Griffiths said cooler air was expected to travel up the South Island on Friday, and reach the lower half of the North Island on Saturday.

"A lot of places should see some cooler temperatures by Saturday – but that front fizzles out somewhere around Taupo, so places in the north may stay more or less warm for the weekend."

And the cool change was only a short reprieve, with more warmth arriving over the country early next week.

Where does climate change fit in?

Meteorologists are understandably cautious about linking any live weather event to climate change.

But climate scientists tell us that we have been seeing a warming trend over recent decades, and that what we're experiencing now is a taste of what's likely to come.

Climate scientist Professor Jim Salinger said average temperatures had risen by some 0.8C in the past four decades, and that temperatures were now about 1C warmer than they were a century ago.

Last summer's heatwave was unparalleled, with the average land surface air temperature reaching 2.2C above the 1981-2010 normal of 16.7C.

"As the country enters another heatwave period for January, land air temperature is running at 1.4C and sea surface temperature is 1.8C above average," Salinger said.

"With further global warming, what we are seeing now and last year's summer could be the norm in the years 2081-2100."