"Generally anywhere inland and sheltered, so there is no sea breeze to cool the temperature."
The hottest spot in the country yesterday was Kawerau in the Bay of Plenty, which peaked at 34.3C at about 4pm in the afternoon.
In Wellington, a 90-year-old temperature record was broken. For about 10 minutes, the suburb of Kelburn rose to 30.3C - the highest since records began there in 1927.
On the roads around Taupō, road surface temperatures hit 60C - hot enough to fry an egg, said MetService.
While this week's heat wave had produced official temperatures in the mid 30s, it had not yet come close to the all-time temperature record of 42.4C in February 1974, in Rangiora.
McInnes said what made this run of hot weather so special was how long it was lasting and its reach.
"Rather than a peak there is just this broad, long-lasting period of hot weather across most of the country, that is what is so remarkable."
There were still "plenty" of hours in the day however, and the heat wave was looking to stick around until Friday in the South Island and Saturday in the North Island, when a southerly change arrived.
The intense heat was being driven by hot air originating in Australia which had parked itself over the country, meaning high temperatures nationwide.
The only places which were below 30C were coastal regions which had been cooled by marine air.
Niwa meteorologist Ben Noll said parts of inland South Island, including Hanmer Springs in Canterbury and Cromwell in Central Otago, could reach 35C or higher by the end of the week.
Noll said the highest temperatures were being recorded inland because they were too far from the coast to be cooled by onshore sea breezes.
For that reason, Napier fell from 35C on Monday to 26C on Tuesday as the easterly from the Pacific Ocean swept in and cooled the region.
The nights have also been offering little relief, with few places across the country dropping below 20C last night, with high humidity.
Auckland was at 20C at 6am, Wellington Airport 21C, while Lower Hutt was the top of the bunch at 22.4C.
Tonight MetService was forecasting much of the same.
