Severe thunderstorm warnings have been issued for the Kāpiti Coast, Horowhenua, Tararua, Palmerston North, Carterton and Masterton and will come into effect from 6pm.
“These thunderstorms are expected to be accompanied by torrential rain,” said MetService.
Torrential rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous.
An earlier red severe thunderstorm warning issued for Hastings and Rangitikei districts has been lifted.
Taumarunui, Taupō, Hawke’s Bay, Taranaki, Taihape, Wanganui, Manawatū, Tararua, Kapiti-Horowhenua, Wairarapa and Wellington are all under a severe thunderstorm watch until 9pm tonight with the potential for heavy storms to develop.
In Gisborne, rain is expected to pour from 9pm tonight with peak rates of 20 to 30mm/h on Monday morning.
MetService meteorologist Claire O’Connor told the Herald the rain comes from a lower pressure system which is descending on New Zealand from the north.
“Given the way the winds go around, it will direct the rain towards the eastern coast so that’s where those warnings come into play there.”
Despite the rain, it’s a sweltering day for much of the country. The hottest today was Masterton which reached a scorching 33C.
In the South Island, it’s slightly cooler with most regions sitting between 20C and 25C. The coldest place in the country is Stewart Island coming in at a balmy 18C.
In Tongariro National Park, lightning has already been detected with the potential for severe thunderstorms to develop in the coming hours.
Further south, there’s a watch of heavy rain for Westland which O’Connor said is caused by a front moving up from the south.
“There’s a bit of precipitation that will impact the West Coast - but it’s fast moving so it won’t have as much impact as the weather the other day.”
On Friday, the West Coast was under a state of emergency due to torrential rain that caused rivers to rise rapidly and forced the closure of State Highway 6 between Haast and Hokitika.
O’Connor said despite more rain being forecast, it wasn’t all bad news - a much-needed break in the high heat and humidity is also forecast to drift across the country in the coming week.
“With this feature moving up the country, these cooler south-[westerlies] go right across the country flushing out the humidity and the heat as well.”
Overnight temperatures could drop into single digits in the South Island this week and Invercargill is looking at a chilly Wednesday - with a high of 13C forecast.
Further north, it’s a similar story with overnight temperatures expected to dip to half of their current temperature.
“The highest [temperature] I can see overnight on Wednesday is 15 degrees,” O’Connor said.
Tropical cyclone strengthening
O’Connor said the tropical cyclone that is strengthening over the Coral Sea is looking like it will hit over the Ditch before it makes landfall in New Zealand - if it hits at all.
The cyclone is forecast to hit Australia on Monday, but O’Connor said it’s difficult to know whether it will strike New Zealand, and how severe it will be if it does.
“It’s going to hit Australia, particularly Queensland but in terms of for New Zealand, it’s still quite far out that a lot of uncertainty and in the models that we can’t say for sure what impact would be for New Zealand if it did come our way.”
Forecasters are closely tracking potential for a tropical low over the Coral Sea to form into a cyclone system, with Australia’s Bureau of Meteorology currently giving a “high” chance (or 55 per cent) of it reaching cyclone strength by early next week.
Niwa meteorologist Ben Noll said that, among other favourable conditions for cyclone development over coming weeks, surface temperatures in the Coral Sea were running warmer than average.
“Basically, west of New Caledonia, extending all the way to the coast of Queensland, we’re seeing moderate to strong marine heatwave conditions.“
Up in the Coral Sea, meanwhile, the marine heatwave could increase the potential for a formed cyclone system to intensify, while contributing more moisture.
“I’d agree it’s too early to say what we can expect with this one,” Noll said of its implications for New Zealand.
