Heavy rain, storms continue for Easter Monday - MetService

MetService says ex-cyclone Tam has been "very gradually losing steam", but warned heavy rain and thunderstorms were still forecast for some parts of the country throughout the day.

Auckland had its second severe thunderstorm warning in as many days yesterday, with one MetService weather station reporting 18mm of rain fell in an hour.

MetService has issued heavy rain alerts for large parts of the South Island - orange heavy rain warnings for parts of Tasman and North Canterbury; and yellow heavy rain watches for Buller, parts of Tasman, Marlborough, North Canterbury, Christchurch and Banks Peninsula.

"Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips," the forecaster warned.

A yellow severe thunderstorm watch is also in place for Bay of Plenty, Rotorua, Taupō, Gisborne, Hawke's Bay and Taihape, with forecasters warning the slow-moving weather system is likely to bring heavy rain, localised downpours, possible hail, and surface or flash flooding.

"These storms may be accompanied by localised downpours with rainfall rates of 25 to 40 mm/h and hail," the forecaster said.

MetService meteorologist Alec Holden told 1News that ex-Cyclone Tam has "very gradually been losing steam, but that doesn’t mean it doesn't have any bite left".

"At about 5pm there was surface flooding in Westport at the top of the South Island as it was clipped by the inner spiral of Cyclone Tam.

"At one point it saw 25mm of rain in an hour. We'd classify that as a downpour, basically meaning anything outside at the time would be drenched."

Holden said that amount of rain was not uncommon for a severe thunderstorm event.

"There is a thunderstorm watch for inland parts of the North Island that goes into effect from 1pm until 9pm today. The area covers from central Hawke's Bay and stretches over Tongariro National Park."

Holden said a high pressure front coming in from the west today will start to have a calming effect on weather conditions, including easing rain.

"The likelihood of thunderstorms greatly diminishes tomorrow (Tuesday), and these are the last severe thunderstorms we’ll see for a while".

NIWA weather said remnants of ex-Cyclone Tam would still bring unsettled weather to central NZ tomorrow.

"Of course... when the long weekend's over, the good weather arrives! High pressure brings a more settled week ahead," it said online.

State Highway 1 near the Brynderwyn Hills, north of Auckland, has reopened after a slip partially blocked the Southbound lane. Both lanes were back to operating as normal.

In Gisborne, New Zealand Transport Agency said State Highway 35 remained closed between Wharf Rd, Hicks Bay and Lottin Point Rd, Pōtaka due to flooding.

"Avoid the area or delay your journey," it said.

North of Westport, Stage Highway 67 between Hector and Mokihinui has also reopened following earlier flooding.

"Take extra care through the area today as surface flooding remains present in areas," NZTA said.

In a post to its social media, Auckland Emergency Management thanked Auckland residents for staying safe during multiple emergency updates and alerts over the long weekend.

"All weather watches and warnings have now expired and the worst of the weekend’s severe weather has passed," it said.

Cyclone Tam and its associated troughs are still expected to affect the country during Sunday night and Monday, bringing heavy rain to parts of the South Island.

Here's a full list of those watches and warnings:

Severe Thunderstorm Watch

Bay of Plenty, Rotorua, Taupo, Gisborne, Hawkes Bay, Taihape - 8 hours from 1pm Monday to 9pm Monday.

Heavy Rain Warning - Orange

Area: Tasman northwest of Motueka - 14 hours from 8pm Sunday to 10am Monday.

North Canterbury about and north of the Waimakariri River - 14 hours from 8pm Sunday to 10am Monday.

Heavy Rain Watch

The Buller District and Nelson/Tasman about and southeast of Motueka, including the Bryant and Richmond ranges and the Rai Valley -13 hours from 8pm Sunday to 9am Monday.

Marlborough (excluding the Sounds, Richmond Range and Rai Valley) - 16 hours from 8pm Sunday to midday Monday.

North Canterbury between the Rakaia and Waimakariri rivers, also Christchurch including Banks Peninsula - 10 hours from 8pm Sunday to 6am Monday.