Pockets of the North Island could slide into drought if a big rainmaker doesn't arrive in the next few weeks, Niwa forecasters say.
The agency's latest monitoring showed a broad swathe of the upper North Island, stretching from Cape Reinga to Coromandel and Waikato, along with parts of Hawke's Bay and Wairarapa, were now experiencing what Niwa termed "very dry" conditions.
The most parched places were the Far North and northern Waikato, now recording a soil moisture anomaly of 50mm below average.
Less than 5mm fell across the North Island over the past week, and the biggest drops in soil moisture were observed in the Far North, as well as central areas from Taranaki eastward to Hawke's Bay.
"There's been an ongoing rainfall deficit over a large part of the North Island since last month," Niwa forecaster Ben Noll said.
"Added to that was some warmth at the end of spring that dried out the ground – we had the warmest November on record."
A continued lack of rain could mean those most affected areas tip into a meteorological drought, an event characterised by a lack of rainfall, along with hot, drying conditions.
"The model guidance we have over the next one to two weeks is supporting that, so we are keeping a close eye on the situation."
While some models indicated a "wildcard" weather system may develop in the tropics and bring down some much-needed moisture, there was no guarantee, Noll said.
"If you get one of those, you can alleviate a big rainfall deficit in a hurry. But if the dry pattern continues – which, by most accounts it looks like it will in the next one to two weeks – I'd expect there will be parts of the upper North Island that are experiencing drought.
"It's also worth considering that, given a large chunk of the country is drier than normal, over the next two weeks, those areas will also turn drier, even if they're not considered to be abnormally dry right now."
Looking beyond the next fortnight, Noll said there were indications of easterly and north-easterly winds sweeping in next month, which could bring rain.
"But, as drought is something that takes a while to come on, it also takes time to depart, so it may take more than one good rainfall event."
Despite the current pattern, Northland Federated Farmers president John Blackwell described conditions as relatively normal for this time of year.
"It's hard to generalise because it's such a narrow peninsula, and one side can be quite different to the other, but, in saying that, I think from a pasture point of view we're on about average for summer," Blackwell said.
But he added the region was still well behind on its average rainfall for the past 12 months, which had affected groundwater levels.
"We've had enough to keep the place green, and grass has been growing pretty well up to until now," he said.
"For us, summer doesn't really start until January. It just depends how long it goes on for. If it's still dry in April and May, that's when it really hurts."
The Ministry for Primary Industries (MPI) has also been watching conditions in Northland over the past few months, and talking with councils and rural groups.
"It is not unusual for Northland to have hot dry summers, and farmers and growers have been planning for these dry conditions," said Cathy Robinson, MPI's acting deputy director-general of agriculture and investment services.
"At this stage MPI considers that the community is generally coping with the dry conditions and is currently classified as localised."
If conditions continued to remain dry the Northland Adverse Events Committee would convene, she said.
Niwa's latest seasonal outlook, covering the next three months, picked temperatures to be near or above average for all of the North Island, near average in the north and east of the South Island, and near or below average for the west of the South Island.
Rainfall was projected to be near or below normal for the north of the North Island, above normal to normal for the west of the South Island, and normal elsewhere.