If you're in eastern Bay of Plenty or Gisborne it's time to batten down the hatches - you're in for a stormy night.

Rain was already falling there and the heaviest downpours were expected in the next half hour or so, MetService meteorologist Lisa Murray said.

"The winds are picking up there as well - there are quite strong southerly winds coming in."

East of Whakatane and coastal Hawke's Bay and the eastern side of the Coromandel Peninsula had all been battered by southerlies and the Central Plateau was now getting some strong winds too.

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A severe weather warning will stay in place for the Gisborne ranges and eastern Bay of Plenty until 6pm, Murray said.

"Rain will continue after that and when I say heavy downpours, I'm talking you could get up to 40mm in an hour up in the ranges especially. Rain that heavy can cause rivers and streams to rise rapidly, also surface flooding."

Main roads in the Bay of Plenty were closed due to severe weather this evening, with State Highway 2 at Waimana Gorge and State Highway 35 between Opotiki and Te Kaha both blocked by slips.

Murray said MetService was concerned that winds would pick up east of Whakatane even more tonight.

"Along the ridge line and any other exposed places can expect gusts of up to 130km/h and considering it's a southerly direction it's quite unusual for them as well - that can also bring down trees as well when the tree roots are used to wind in a different direction."

The worst of the weather should ease overnight, Murray said.

"Although places like Gisborne and the northern part of Hawke's Bay will get some rain for a time first thing in the morning, it does pull away quite quickly with the odd shower left there.

"But those southerly winds do stick around for that eastern coastline of the North Island tomorrow and will gradually ease off later on in the day."

The good news weather wise was that a ridge of high pressure was moving in from the Tasman sea.

"It's currently over the South Island - like the West Coast is basking in sunshine, if you can do that in cooler temperatures. They even got a 17C today," Murray said.

"That ridge will push on to the South Island over the rest of New Zealand, so a lot of places will be fine tomorrow."

But eastern areas and Wellington were likely to get a bit of cloud or the odd shower.

Most of New Zealand should get a cool but mainly fine Mother's Day, Murray said.

"There's a few showers around the country here and there but not much so most people will be able to get out. There'll be plenty of dry spells and even sunshine."

And while Kiwis could expect a pretty good start to the week weather wise on Monday, a low will sweep in on Tuesday, bringing rain and wind midweek.

Saturday's forecast
Whangarei: Chance morning shower, then fine weather and fresh southerlies easing. High of 17C
Auckland: Fine. Fresh southerlies, easing evening, 15C
Hamilton: Fine. Fresh southerlies, easing in the afternoon, 15C
Tauranga: Fine. Fresh south easterlies, easing in the afternoon, 16C
Wellington: Cloudy periods, with a few showers until evening. Strong southerlies, easing in the afternoon. 11C.
Christchurch: A few showers clearing in the morning and becoming fine. Southerlies dying out in the morning, 11C
Dunedin: Morning cloud clearing to a fine day. Westerlies dying out in the morning and 13C
(Source: MetService)