MetService predicts high confidence of warnings for Northland and moderate confidence for Auckland and Coromandel.
The Tasman Sea low may weaken on Friday, but heavy rain warnings likely remain for Northland and Auckland.
The first tranche of weather alerts has been issued ahead of 38 hours of heavy rain and gales set to lash the upper North Island from midday Wednesday.
MetService put out a heavy rain watch for Northland, beginning from 6am Wednesday, Auckland and Great Barrier Island and the Coromandel Peninsula, lasting to 3pm Thursday.
“Rainfall amounts may approach warning criteria - and possibly exceed them,” the forecaster said.
“Streams and rivers may rise rapidly. Surface flooding, slips, and difficult driving conditions [are] possible. Clear your drains and gutters to prepare.”
Strong wind watches have also been issued for Northland, Auckland and Great Barrier Island, with gales expected to threaten powerlines, trees and unsecured structures.
A slow-moving subtropical low is forecast to track southward over the northern Tasman Sea, delivering strong, moist easterly winds to the northern North Island in the lead up to Easter.
MetService meteorologist Juliane Bergbolt told the Herald this will mean heavy rain for Northland, Auckland and Coromandel on Wednesday.
MetService said there is a high confidence that warnings will be issued in Northland for heavy rain and severe gale easterlies.
“For Auckland, the Coromandel Peninsula and western Bay of Plenty there is moderate confidence that a rain warning will be needed,” it said on its site.
“There is moderate confidence that a wind warning will be needed in Auckland, Coromandel Peninsula and eastern Waikato and low confidence the warning will also cover the rest of Waikato.”
Bergbolt said winds could reach up to 90km/h in warning or watch areas with frequent gusts of up to 100km/h.
The top of the North Island is set for a drenching when heavy rain and gales pass through on Wednesday, Thursday and Friday. Photo / MetService
On Thursday, the large low is forecast to remain over the north Tasman Sea where it will direct a strong flow over New Zealand.
There is a high chance of heavy rain and severe gales in Northland, Auckland, Coromandel and the northern Bay of Plenty, according to MetService.
There is a moderate chance of the same conditions for Waikato, the southern Bay of Plenty and the Eastern Cape.
On Friday, the Tasman Sea low may weaken slightly.
However, MetService said there is a good chance that heavy rain warnings will stay in place for Northland and Auckland, excluding Great Barrier Island.
For Great Barrier Island, the Coromandel Peninsula, Bay of Plenty, and northern Gisborne/Tairāwhiti, there’s a high chance of heavy rain warnings, and a low chance that the northeast winds will become strong enough to trigger a severe gale warning.
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