The Coromandel and parts of western Waikato have been added to the watch.
This afternoon, MetService issued a severe thunderstorm watch for the Bay of Plenty and Rotorua between 10pm tonight and 5am on Monday - with rainfall of 40 millimetres an hour possible.
MetService also issued orange heavy rain warnings for southern holiday hotspot Nelson, as well as Taranaki, lasting the next two days; and issued watches for the Bay of Plenty, Kāpiti-Horowhenua, Tararua, Wairarapa, Marlborough and Westland.
“If you’re holidaying in [those] regions, it’s not going to be pleasant,” MetService meteorologist Karl Loots said, warning up to 100mm of rain could fall in the worst-hit areas.
“That is particularly heavy rainfall,” he said.
The rain could quickly cause streams and rivers to rise, surface flooding and slips, MetService said.
“Always drive to the conditions, and also stay up to date with the latest forecast, because we’re constantly updating these watches and warnings,” Loots said.
Hailstorms, gusts up to 100km/h and tornadoes could accompany the “squally” thunderstorms in the upper north, MetService said.
“A few of the thunderstorms could become severe later today. Forecasters will be monitoring the situation throughout the day.”
The thunder was also expected to roll into the Coromandel, Rotorua, Taupō and North Taranaki on Sunday evening, with the rest of the central North Island and upper South Island at risk.
Loots said the warning for Nelson lasted until Tuesday evening, with the highest rainfall, up to 20mm an hour, expected early tomorrow morning.
“It’s not a particularly good place to be for a holiday at the moment,” he said.
In Taranaki, up to 25mm an hour was expected - “and maybe more”, MetService said. The warning there lapses on Monday morning.
“Into tomorrow, it becomes a lot more chaotic, and there’s a lot more widespread convective activity during [the day]. The main focus areas will be southern Waikato down to the Kāpiti Coast,” Loots said.
“[A watch for] the Richmond Ranges between Nelson and Marlborough will be from 7pm this evening until later on Tuesday, 11pm,” he said.
A heavy rain watch was issued for the Bay of Plenty ranges from 1am until 9am on Monday, with 25mm of rain an hour possible there.
A watch for Tararua, where rain could also reach warning criteria, is in place from 1pm until midnight on Monday.
Meanwhile, in Auckland, showers should clear on Monday afternoon and turn fine with a high of 24C, while Tuesday could see showers develop and stick around from the morning with a high of 22C.
“Periods of rain [in Westland southwards] may approach warning criteria. Watches in place [there] are from 8pm [today] until 6pm on Monday.”
