MetService meteorologist Ciaran Doolin said gusts of up to 100km/h had been recorded in Auckland this evening.
The winds have left 942 residents in Mairangi Bay without power. Vector estimates the power will not be restored until Thursday.
A Northern Fire Service spokesman said the Fire Service had been called about two trees down in Auckland; one in Glen Eden and one in St Heliers.
Gusts of up to 100km/h had also been recorded in the Coromandel, while winds of up to 120km/h had been recorded in Northland.
Wind speeds were also starting to pick up in Waikato, Taranaki and the Manawatu, he said.
A few stations around Nelson had recorded more than 25mm of rain in an hour this evening.
"There's also been 10 to 11mm an hour recorded at a Northland station, while it's just starting to rain in Auckland.
"It should pick up in Auckland in the next couple of hours.
A thunderstorm watch is in place for Northland, Auckland, Great Barrier Island and Taranaki.Rain of 150mm combined across the Northland region was expected over an 18-hour period, MetService meteorologist Lisa Murray said.
Coromandel Peninsula could have 80 to 100mm over the same time period.Ms Murray said rainfall of this intensity could cause surface flooding and advised motorists to take care when driving.
Previously in conditions like these, power lines have gone down, tree branches have fallen, and unsecured trampolines can take off, she said.
The severe weather would subside by tomorrow and there would be settled weather for the long weekend, Ms Murray said.
"There's an improving trend for the Easter weekend with more settled weather and cooler air," she said.
WeatherWatch head analyst Philip Duncan said severe weather would be in "pockets" or "hit and miss".
"We see areas of unstable weather where pockets of sub-tropical energy will bubble up and create torrential rain and maybe damaging winds - but around that it may just be a bit windy and drizzly."
Winds are currently blustery in Auckland, eastern Waikato, western Coromandel Peninsula and parts of Northland.
"Winds may increase further overnight, and among some of the biggest cloud build-ups - or downpours - there may be stronger wind gusts over 100km/h on Thursday morning," he said.
Mr Duncan said while the bulk of the rain would be "light and drizzly" some would be "quite explosive sub-tropical downpours".
It could be heavy enough to cause localised flooding, he said.
"The front may be very dramatic out at sea, then weaken as it moves in, then across Thursday may again grow in energy over parts of the North Island, before clearing away overnight tomorrow night."
Whangarei
Tomorrow - Morning downpours, NE gust 100 km/h, to showers and westerly. 26C.
Friday - Fine spells, possible shower. Light winds. 25C.
Auckland
Tomorrow - Morning downpours, NE gust 100 km/h, to showers and westerly. 24C.
Friday - Fine spells. Southwest breezes. 24C.
Hamilton
Tomorrow - Morning downpours, to showers as strong NE changes westerly. 24C.
Friday - Fine spells, possible afternoon shower. Southwest. 25C.
Tauranga
Tomorrow - Downpours, to showers afternoon as strong NE changes westerly. 24C.
Friday - Few showers from afternoon. Westerlies dying out. 25C.
Wellington
Tomorrow - Heavy rain, northerly. Fine afternoon. Late southerly rain. 22C.
Friday - A few morning showers. Strong southerlies easing. 17C.
Christchurch
Tomorrow - Rain, then showers, heavy evening. Strong northerly turns southerly. 26C.
Friday - Becoming fine. Southerlies dying out. 16C.
Dunedin
Today - Showers, fine evening. Southwesterly change. 21C.
Friday - Mainly fine. Southerlies dying out. 15C.
- Source: MetService
