Cyclone Fehi to bring deluge, plummeting temperatures to NZ

Make the most of the sweltering weather on Wednesday - because a former tropical cyclone barrelling towards New Zealand is set to end it rather abruptly.

Category One Tropical Cyclone Fehi formed near New Caledonia earlier on Monday, and MetService says the "major storm" will lash the South Island on Thursday and early Friday, bringing "possible damaging gales".

Temperatures are set to plummet by 20degC by Friday morning.

The combination of strong winds, heavy swells and high tides could cause coastal inundation on the West Coast and Nelson on Thursday.

A heavy rain warning is in place for Westland and Fiordland for Thursday night.

Southern regions may even see snow on peaks in Westland and Fiordland on Friday morning, MetService told NZME.

It'll be a stark contrast to this week's heatwave which saw record-high temperatures on Tuesday, with Wednesday also forecast to be a scorcher.

WeatherWatch says the warmer-than-usual waters around the country will help fuel the storm, and keep very heavy rain and winds going.

However the waters are cooler where the storm has come from so it has lost tropical status as it moves towards the country.

Cyclone Fehi is expected to weaken as it moves across New Zealand, but holidaymakers, trampers and those in rural areas should be well aware of the potential for severe weather from the cyclone.

As with any tropical storm, "nothing is locked in," WeatherWatch says.

The storm has little to block it, land or pressure-wise, as it tracks south toward New Zealand and is expected to curve around the western side of the large high that is currently over the country.

Thursday is expected to be a "very wet day" in many regions, but expected to clear on Friday.

Rain may linger longer in the North Island, as it breaks away from the low and gets slowed down by the high to the east.

There is also a chance of flooding from the low and some wind damage, and seas are also expected to get rough in western areas later this week.

MetService advises South Islanders to keep an eye on the latest weather warnings.