Northland is likely to experience extended dry spells this winter that can potentially affect river and dam levels heading into summer.
Niwa's seasonal climate outlook for June to August predicts rainfall to most likely be near normal. However, there may be brief spells of heavy downpours that can cause widespread flooding, as happened in July last year.
Niwa is not predicting a colder-than-average winter.
Temperatures are about equally likely to be above average or near average, soil moisture levels are equally likely to be near normal or below normal, and river flows are most likely to be near normal.
Niwa climate scientist Ben Noll said adverse weather events such as the big deluge in July last year across Northland that caused widespread flooding and slips were also likely this winter.
"The soil moisture level in parts of Northland are still a bit down. Intermittent rain could be followed by long periods of dry spell that will bring chilly mornings.
"There are big areas of high pressure system in New Zealand, as well as remnants of the La Nina from the summer months, that could contribute to long periods of dry spell this winter," Noll said.
He said rain developing in Northland this weekend would help to raise river and dam levels but cautioned it would be a gradual build-up over the next three months.
Noll said there would still be days when temperatures would be in the early 20s.
Demand for winter firewood in Whangārei began early this year.
Tree Wise owner Aaron Bradley, who supplies to households in Whangārei and Auckland, said the demand started months before winter.
"I get rid of all my wood between October and February and whatever is here will all be gone by the end of winter. I tell people to order them early before they get wet."
Federated Farmers Northland dairy acting chairman Matt Long said the general rule was that dry weather made the work of farmers easier, as long as there was steady rain in between.
"Rain along the east coast has been fairly average the past couple of weeks but the ground conditions are still pretty dry. Having said that, we do need a decent amount of rain before the next summer."
The weather outlooks are the result of the expert judgment of Niwa's climate scientists. They take into account observations of atmospheric and ocean conditions and output from global and local climate models.
The presence of El Nino or La Nina conditions and the sea surface temperatures around New Zealand can be a useful indicator of likely overall climate conditions for a season.
There are currently no water restrictions in Northland, except in Dargaville and Baylys Beach where Level 2 restrictions are in place.
In Whangārei, the Whau Valley Dam level is tracking at just 54 per cent, while Wilson's Dam is at 68 per cent.