Although the initial burst of rainfall this morning is not expected to be as heavy as MetService previously forecast, up to 130mm of rain could fall in the Bay of Plenty ranges by mid Thursday morning. In the ranges of Taupo and the Tongariro National Park, around 90 to 110mm is possible.
The rain should be heaviest this evening or early Thursday morning, MetService said.
WeatherWatch analyst Philip Duncan said he had received reports of heavy rain from Whangarei right down to Manuwatu.
"It's pretty nuts. Certainly in Auckland it has been torrential at times and we've got gales as well in exposed places."
Mr Duncan said the heavy rain should ease in Auckland, Waikato and Northland overnight.
"I think it will get heavy this afternoon or this evening, and it should ease - tomorrow looks much better.
"We're only getting the edge of it really, the Bay of Plenty are going to cop a lot more than we are."
Mr Duncan said the rain is setting in the Bay of Plenty and should peak overnight. He said it will ease tomorrow afternoon.
Bay of Plenty Regional Council flood duty manager Graeme O'Rourke said there were pre-emptive warnings on all major river schemes.
"A number of precautionary measures have been taken with pumps and drainage systems in preparation for heavy rainfall and staff will be on standby throughout the night to respond if required," Mr O'Rourke said.
"Because of the already saturated catchments, river levels may rise quickly so farmers should move to stock to higher ground now if they haven't already," said Mr O'Rourke.
Mr Duncan said the weather conditions were particularly hazardous for driving, with heavy rain, gales and potential flooding, with the possibility of slips.
"The good news is this is the last sub-tropical low we are going to have for at least 10 days. So for the first time in almost a month our weather pattern goes to what it should be for this time of the year, that's more of a west to southwest direction.
"The next lot of rain makers that are going to come through over the next week or two are mainly going to hit the West Coast and Southland, not so much the North Island and certainly not the Bay of Plenty and the Hawkes Bay.
"The reason why this one is so humid is this low is tapping into air that is right up by New Caledonia. It's very out of character for this time of year to have so many of this warm lows coming through, but this does look like it will be the last one for at least for the next 10 days."
