Forecasters are tracking an active tropical cyclone potentially threatening New Zealand, while a subtropical low is set to unleash heavy rain and strong winds from this evening.

MetService said a subtropical low is expected to approach the far north of the North Island overnight and will move southwards, reaching the upper South Island tomorrow evening.

Heavy rain and strong east to northeast winds are forecast ahead of the low, with easterly gales expected in Northland.

A string of severe weather watches and warnings has been issued, with the system set to impact the country until early Thursday.

Heavy rain on the way

MetService meteorologist Alec Holden told the Herald the subtropical low is attached to an older low.

“By their powers combined, they are still making little headway, mainly because there is a very large high-pressure system to the southeast of the country that is slowing both of their movements down,” Holden said.

However, he said conditions are expected to change because the subtropical low and its associated fronts are forecast to move over much of the country from tomorrow.

“This subtropical feature [is] just funnelling all this water straight from somewhere not far off of Vanuatu and then bringing that down over New Zealand and just wringing it out like a sponge,” Holden said.

Periods of heavy rain are expected for the upper North Island and the upper South Island. Photo / MetService

• Northland on alert again with 18-hour rain warning and gale-force winds

Severe weather watches and warnings

An orange heavy rain warning is in place for Northland from 10pm tonight until 4pm tomorrow.

A heavy rain watch is in place for Auckland and Great Barrier Island from 9am tomorrow until 9pm.

MetService said this rain will mainly affect north of Papakura.

Holden said Auckland will experience the worst of the rain from mid-morning to late afternoon tomorrow.

The Coromandel Peninsula is under the same watch from noon tomorrow until 3am Wednesday.

The Bay of Plenty west of Whakatāne, including Rotorua, is under the same watch from 3pm tomorrow until 6pm Wednesday.

A heavy rain watch is also in place for the Bay of Plenty about and east of Whakatāne, from 3pm Wednesday to 9am Thursday.

Tasman, northwest of Motueka, is also under a heavy rain watch from 9pm tomorrow until 6am Wednesday.

MetService has issued a strong wind watch for Northland from 3am tomorrow until 4pm.

These warnings come after the Northland region recently suffered widespread flooding, with settlements in Whangārei and the Far North cut off and more than 80 homes damaged.

Both districts declared states of emergency.

Two active tropical cyclones

MetService said it is tracking two tropical cyclones in Pacific waters.

A “severe” category 3 tropical cyclone named Maila is currently slow-moving in the Solomon Sea.

Another category 2 tropical cyclone named Vaianu is currently located about 600km northwest of Nadi in Fiji.

Holden said MetService has been keeping an “extremely close” eye on them, especially Vaianu.

“That one is in an area where it could theoretically come and take a New Zealand holiday. However, it’s still at this point far too early to say anything with particular confidence,” he said.

Holden said the models have been “extremely jumpy” in terms of where the cyclones are predicted to end up.

“Hopefully, fingers crossed, it’ll sail far out to the east of us and give Bay of Plenty maybe a bit of a rain tickle,” he said.