"Parts of the Coromandel may even see close to 30mm to 40mm, especially over the hills, which is not what it needs."
In Auckland, where water restrictions remain in place amid an ongoing severe drought, about 10mm to 20mm could be expected.
MetService reported the broad low would move on to central New Zealand on Thursday, bringing rain to many areas, followed by cold southerlies.
The low then moved away to the northeast on Friday and early Saturday as a ridge of high pressure builds over the South Island.
There was low confidence that rainfall accumulations will reach warning criteria in Fiordland on Wednesday and also for Nelson, northern Marlborough, the Tararua Range, Taranaki and the central North Island high country through to the eastern ranges of Bay of Plenty late Wednesday and Thursday.
For Canterbury north of about Ashburton, southern and eastern Marlborough, Wellington and southern Wairarapa, there was low confidence of rainfall amounts reaching warning criteria on Thursday.
On Saturday, the ridge moves on to the North Island, while a cold front moves on to the South Island with no associated severe weather at this stage.
The forecast downpours come after Auckland received some welcome rain over the long weekend.
Between 9am Friday and 9am today, about 45mm fell over Kumeu, along with 32mm in central Auckland, 16mm at Mangere, 35mm at Albany, 48mm at Leigh and 21mm at Pukekohe.
Taking in the rain that has fallen since last Tuesday, Kumeu received 77mm, Auckland 55mm, Albany 63mm, Leigh 50mm, Mangere 23mm and Pukekohe 29.8mm.
"More rain was observed in this past seven-day period at our Mangere and Albany climate stations than what was observed for the months of Feb and March combined," Brandolino said.
Auckland's dams have slightly benefited – about 78mm fell over the Lower Huia Dam in the Waitakeres over the past seven days, while the Upper Mangatawhiri Dam received about 65mm.
Yet total water storage was still sitting at just 44.5 per cent, compared with the 77 per cent average for this time of year.
Brandolino said there was a long way to go to Auckland making up a rainfall deficit that was running at around 200mm.
And following several periods of rain over the next seven days, an extended period of dryness was on the cards, he said.
In the longer term, the same climate conditions that had contributed to dryness over much of New Zealand were expected to influence our weather for at least the first half of the winter season.
Across winter, air pressure was forecast to be higher than normal to the north of, and sometimes over New Zealand.
As a whole, air temperatures were most likely to be above average in the east of the South Island and about equally likely to be near average or above average in all other regions.
Rainfall levels, meanwhile, were most likely to be below normal in the east of both islands, near normal in the west and north of the South Island, and about equally likely to be near normal or below normal in the north and west of the North Island.
