Photo: RNZ / Rebekah Parsons-King
People in the upper North Island are being warned to brace for heavy rain and gale-force winds as a subtropical low sweeps over the top of the country.
MetService meteorologist Clare O'Connor said an orange heavy rain warning and a severe thunderstorm watch were in place for Northland this afternoon, followed by a strong wind watch later tonight.
She said people in affected areas should clear their drains and gutters, and secure any objects that could be blown away.
O'Connor said the current forecast was for 90 to 120 millimetres of rain in Northland between 3pm today and 10am tomorrow.
The real risk, however, was from localised downpours caused by thunderstorms.
A severe thunderstorm watch was in place from 11pm tonight until 8am tomorrow.
"So even if you're not seeing lightning or hearing thunder, these downpours could bring up to 60 millimetres an hour. That is a very large amount of rain to fall in a very short time, and would be likely to cause flooding," O'Connor said.
"So keep up to date, clear out your drains if you're able to, and make sure anything you have outdoors is strapped down or heavy enough to not get blown away in potentially 100 kilometre an hour gusts of wind."
O'Connor said torrential rain could cause surface or flash flooding, especially in low-lying areas near streams or in narrow valleys, and could also lead to slips.
Driving conditions would be hazardous with surface flooding and poor visibility.
She said the thunderstorm risk would ease from the north during the morning, but continuing isolated thunderstorms were possible in southern and western Northland tomorrow afternoon.
According to a MetService weather update, the heavy rain was expected to reach Auckland and Coromandel early tomorrow morning.
An orange heavy rain warning was in place for the Coromandel Peninsula from 6am on Tuesday until 9pm that evening, and a heavy rain watch for Auckland and Great Barrier Island from 4am to 4pm on Tuesday.
Next in the firing line would be the Tairawhiti region, around and north of Tolaga Bay, where a heavy rain watch was in place from 3pm on Tuesday to 9am on Wednesday.
There was a moderate chance that could be upgraded to a warning.
Meanwhile, a strong wind watch was in force for Northland from 1am to 8am on Tuesday, and for Auckland, Great Barrier Island and Coromandel Peninsula from 4am until noon on Tuesday.
Easterly winds could approach severe gales in exposed areas, MetService warned.
According to MetService criteria, anything from 6 to 25mm of rain per hour was classed as heavy.
Rainfall of 25-40mm/hr was regarded as a downpour, while anything over 40mm/hr was torrential.
Meanwhile, Northland Civil Defence said low tides and river levels could work in the region's favour.
Spokesman Zach Woods says Northlanders should be prepared for downpours, given MetService's upgrading of its heavy rain watch to an orange warning.
He said the worst of the rain was expected to hit when the tide was out, reducing the risk of flooding.
"We're keeping an eye on the situation. However, a lot of it is expected to go through this afternoon and overnight when the tides are favourable, and a lot of our rivers are actually running at quite low flows at the moment. So that's a relief in terms of potential for any river flooding," he said.
"I think a lot of people, especially those on tank water and those in rural communities, will be pretty happy with getting a bit of rain. We've been very dry up here lately. Let's just hope it's not too much of a good thing."
Woods urged Northlanders to keep up-to-date with weather forecast, and to take extra care on the roads because hazards such as surface flooding and slips could happen quickly.
Regional council hydrologists would continue to monitor the situation overnight, he said.
Following the sudden turnaround in weather conditions, Fire and Emergency has relaxed fire restrictions in Northland, returning the region to a restricted fire season from what was effectively a total fire ban.
Any previously issued fire permits that had been suspended during last week's soaring fire risk were reinstated as of Monday morning.
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