Weather: Severe storm watch, heavy rain loom for Auckland, regions

The heaviest rain from a complex trough going over the top of the country is likely to affect the north of the North Island, and the north and west of the South Island.

A number of heavy rain watches and warnings are in place around the country from Thursday night until Friday.

Affected residents are being advised to clear drains and gutters, avoid low-lying areas and drive cautiously.

Local Civil Defence and emergency management groups for Northland, Auckland, Waikato, and Bay of Plenty are reiterating MetService's information on the watches and warnings.

MetService said the weather systems from the Tasman Sea could affect the country into next week.

Meanwhile, National Institute of Water and Atmospheric Research said low pressure was forecast to stall in the Tasman Sea for the next week.

"Areas of vorticity, or atmospheric spin, will 'pinwheel' around the low, bringing semi-regular rounds of rain & thunderstorms to many regions of the country, starting tonight."

What's expected in each region?

• Between 8pm Thursday and 1pm Friday, localised downpours of 25-40mm/h may affect parts of Northland at times. The thunderstorm and downpour risk initially starts in the Far North this afternoon, then spreads southwards to other parts of Northland this evening. The storm watch for the region is in place until 11am Friday.
• In Auckland, localised downpours between 25-40mm/h are possible with severe thunderstorms, this might cause some surface flooding in some areas if these totals are reached. The heavy rain watch is in place from 8pm Thursday until 4pm Friday. The severe storm watch is in place from about 10pm tonight and 5am Friday.
• An orange heavy rain warning is in place for Bay of Plenty and Rotorua from 1am until 9pm Friday. Expect 80 to 110mm of rain to accumulate. Peak rates of 15 to 25mm/h, but rates of 25 to 35mm/h possible in localised downpours and thunderstorms.
• A heavy rain watch from 3am to 9pm Friday is in place for Taupo, with periods of heavy rain expected. Rainfall may approach warning criteria. Thunderstorms are also possible.
• Mt Taranaki can expect the same as Taupo - except their watch is in place from 1am Friday to 7pm.
• An orange heavy rain warning is in place for Tasman northwest of Motueka from 8pm Thursday to Friday to 8pm. Expect 120 to 150mm of rain to accumulate. Peak rates of 15 to 25mm/h. Meanwhile, a heavy rain watch is in place southeast of Motueka and Marlborough northwest of the Wairau River from midnight until 8pm Friday.
• A heavy rain watch is in place for Fiordland north of Doubtful Sound and the ranges of the Westland District from Thursday 8pm until Friday 5am. Periods of heavy rain are expected, and amounts may approach warning criteria
• A road snowfall warning is in place for Milford Road (SH94) near the tunnel from 4pm until 2am Friday.

Warning to Aucklanders

Auckland Council emergency management general manager Adam Maggs said residents should take precautionary measures before the rain was expected to set in from about 8pm.

"Just check the drains around the property, if [residents have] got things that are loose and laying around, tuck them away, just do some of those checks that you'd do if you know some weather's coming in," he said.

"We're not expecting huge volumes of rain, but we are expecting lots of showers and messy weather coming from the north and the east."

The northern and eastern parts of the region could see more rain than other areas, Maggs said.

The rain would likely exacerbate already damp conditions, he said.

"Soils are saturated, so we're going to see run-off off the land, and there will be localised flooding likely," he said.

"Water's got nowhere to go except basically run-off, so we're likely to see, even with reasonable numbers, some localised flooding on some of our roads, some of the areas that would typically see surface flooding, might see that surface flooding until it's got time to drain away.

"We're not talking huge volumes of rainfall, just the fact that, at this time of year, we're already pretty wet anyway and we've just got more rain coming."

Residents should report any blocked drains or fallen trees to the council.

"If people see trees down, report a problem on the Auckland Council online website, it's important, and any blocked drains, feel free to call Auckland Council on 09 301 0101, and we'll get that resolved," Maggs said.

He warned rain could still be pouring on Friday morning, and advised motorists to take care on the roads and drive to the conditions.