Wild winds are set to crash into the capital and Wairarapa overnight, MetService warns.
A weather warning has been issued for the lower North Island as a front pushes up the South Island.
"We're expecting the wind to reach its full fury, with gusts of around 120km/h this evening and probably easing away not long after dawn tomorrow,'' meteorologist Ian Gall said.
The north westerly wind had already reached gale force by this afternoon in some exposed areas around Wellington including at Mount Kaukau, the Rimutaka ranges and Mana Island.
Heavy rain hit Fiordland, Westland and the Southern Alps today and MetService advised trampers and holiday-makers that rivers and streams could rise rapidly, and that surface flooding and slips were possible.
By tonight 70 to 90mm of rain was expected in the Westland ranges with 120 to 140mm over the higher parts of the Southern Alps.
Main centre forecast for the next two days:
* Auckland: south west wind change with some showers tomorrow. Tuesday, mostly fine, with evening cloud.
* Hamilton: light rain tomorrow morning. Fine weather Tuesday.
* Wellington: mainly fine, with strong winds continuing tomorrow, which ease on Tuesday.
* Christchurch: cloudy periods with some showers tomorrow. Tuesday fine with light winds.
* Dunedin: cloudy with showers into the evening tomorrow and cloudy periods with fine periods on Tuesday.