The danger of the powerful gusts is elevated by wet soil from recent deluges, the National Institute of Water and Atmospheric Research (Niwa) said.
MetService said the winds would particularly impact Muriwai, recently reopened Piha, Karekare and the Awhitu peninsula - all badly hit by Cyclone Gabrielle in February.
The buffeting winds and showers are brought by a moisture-laden, intense low-pressure system rushing over the country from the Tasman Sea since Thursday.
Gales could create huge ocean swells around northern regions of the country, with five-metre waves already recorded today and “larger waves to come”, MetService said.
“Take extra care about the coasts. Keep an eye on these wind watches and warnings over the weekend,” the forecaster said.
MetService said the low-pressure system was seen on satellite imagery surrounded by a “koru of cloud” today.
The strong wind watch in Northland lasts from 3pm today until 9am Saturday.
In Auckland, including Great Barrier Island, the watch lasts from 9am until 9pm tomorrow.
In western and central Waikato and Waitomo the watch is in place from midday Saturday until 3am Sunday.
For the Bay of Plenty and eastern Waikato, meanwhile, a strong wind watch was set to lapse about 3pm Friday.
In Taumaranui, Taupō, Taihape, Whanganui, Manawatū and Hawke’s Bay, the watch begins at 6pm Saturday, lasting until 9am Sunday.
A watch in Taranaki begins at 8pm today and lasts until 9pm Sunday.
The double-whammy wind watch and heavy rain warning in Gisborne began at 8am Friday. The watch should end at 7pm and the rain warning should end at 6pm.
Up to 90mm of rain was tipped to fall about the ranges, along with localised downpours associated with thunderstorms. MetService warned of quickly rising streams and rivers, flash flooding and slips.
Further south, in Tasman west of Motueka, a heavy rain watch is in place for 31 hours from 8am today until 3pm Saturday. Up to 160mm of rain could fall in that time.
Slips are possible there, along with surface flooding from intense rainfall during thunderstorms this afternoon. Up to 25mm of rain was possible in an hour.
MetService said the weather should improve on Sunday but frequent showers were likely in the west of both islands until “at least” early next week.
