A forecaster is picking a scorching start to November, ahead of a summer season likely to lean toward the warmer side of normal.
This weekend, temperatures in some eastern areas could be approaching record figures, thanks to a mass of hot air flowing across from Australia.
"As we go through the next few weeks, we'll find that the start of November could be ridiculously hot and dry – and the second week of the month and even after could be pretty warm," Niwa forecaster Ben Noll said.
Temperatures were forecast to hit 31C in areas including Blenheim, Christchurch and Hastings on Sunday.
Other weekend hot spots included Gisborne (29C on Sunday), Masterton (30C on Sunday), Alexandra (29C on Sunday), Napier (29C on Sunday) and Tauranga (27C on Sunday).
In Auckland, however, the mercury was forecast to climb only as high as 20C on Sunday, and 21C on Monday.
• Weather causing chaos in Christchurch
• Weather: Mainly fine for the North Island ahead of soaring temperatures nationwide this weekend
• Labour weekend weather: Hot days ahead for some, wet for others
• Wild weather to hit: Rogue waves, heavy rain, hurricane-force winds
Noll said parcels of warm air coming across the Tasman Sea would be "supercharged" as they hit the South Island and then descended downward to lowland areas – even returning to a similar state they were over drought-stricken Australia.
"That makes the upward potential for temperatures here in New Zealand to be even a little higher – we're talking near-record territory in some locations."
It came as some places, such as the interior parts of southern Canterbury and Otago, had been seeing abnormally dry conditions over recent weeks.
There was also some dryness in the Marlborough region, as well as in Wairarapa and in the Far North.
"We need a couple of good, warm, rainmakers in November or early December to set us up nicely for summer," WeatherWatch head forecaster Philip Duncan said.
"Pasture growth rates are already slowing down in some regions due to the uptick in dry weather lately and the next week ahead looks much drier than normal."
Duncan said that, normally by now, rainfall totals would be higher in many northern regions and spring often brought a final top up.
"Southland and the West Coast have had a fair bit of rain lately and some surprise areas like Hawke's Bay too," he said.
"But overall while soil moisture levels aren't too bad it's the water levels deep down and in our waterways and lakes that may be more of an issue in the hotter, drier, months ahead."
Over winter, Aucklanders were asked to save water and achieved a 2.5 per cent drop in usage.
"Some good rain has fallen since winter in our largest city but things are now leaning dry again," Duncan said.
"Already gardens are drying out and lawns have stopped growing as fast. People will be using their hoses and sprinklers more and more."
Here comes summer
Over the next three months, meanwhile, rainfall levels were equally likely to be near or below normal for the north and east of the North Island, near or above normal in the west and east of the South Island, and most likely near normal everywhere else.
And in the South Island and western North Island over the next month and a half, there was also a risk of big downpours – and potentially even a higher threat of flooding events.
Niwa's just-issued outlook for the November to January period also picked little chance of cooler summer, with average or above average temperatures were equally likely across New Zealand.
The exceptions to that general trend were eastern regions of the North Island, which would most likely see above average temperatures, and western areas in the South Island, where conditions would be near normal.
And Niwa projected more of those big westerly air flows from Australia – potentially warming up surface temperatures in the Tasman Sea and New Zealand's coastal waters again, and in turn driving temperatures even higher.
The big picture
Over the past two months, the big climate driver playing with our weather has been something called the Indian Ocean Dipole, or IOD.
The IOD typically had three phases - neutral, positive and negative – and the current system had been in a near-record positive state.
In a positive phase, westerly winds weakened along the equator, allowing warm water to shift towards Africa.
Changes in the winds also allowed cool water to rise up from the deep ocean in the east.
This ultimately set up a temperature difference across the tropical Indian Ocean, with cooler than normal water in the east and warmer than normal water in the west.
In Australia, this had already contributed to the unusual dryness much of the country had been experiencing.
This seesaw-like system was expected to keep influencing our weather over coming months, but slowly fade as summer bedded in.
At that point, warmer sea surface temperatures and El Niño-like conditions would play a bigger part.
While ocean temperatures out in the equatorial Pacific have been in what's called an ENSO neutral state – meaning neither La Nina or El Niño – Niwa expected patterns to lean toward the latter.
In New Zealand, El Niño typically meant farmers in the western, wetter parts of the country often faced significant damage to pastures from too much rainfall, and it was also harder for stock to thrive in the constant wet.
Those in the east, faced with dry conditions, needed to consider food availability for stock.
But Noll didn't expect anything like the full-blown El Niño conditions that have fuelled severe droughts in the past.
"It's a very weak ENSO state – but occasionally we might have some El Niño-like vibes."
The risk of ex-tropical cyclones over the wider period wasn't any greater than normal, with the average one event expected between now and April.
But Noll said that situation might change in the back-half of summer, depending on what played out in the western Pacific.