A strong cold flow coming from the Southern Ocean is set to spread up the country, bringing strong gusts, rain and swells from Sunday to Tuesday.
This will bring relief from warm, muggy nights over the North Island on Sunday - but also means a cold change and rain in its wake.
"A front moves over the South Island from the west today then across the North Island on Sunday, bringing a period of brief heavy rain and strong north to northwesterly winds," MetService says.
"A trough then crosses the far south from the west on Sunday bringing about a strong southwest change."
NIWA's modelling shows that much of the South Island has a high chance of gusts over 70km/h.
"Our experimental ensemble modelling is showing us that a cold front will cause areas of gusty winds in the South Island tonight, which will spread to the North Island tomorrow," NIWA states.
MetService is forecasting long period westerly swells rising to 4.5 metres along the Westland coast, which will also affect also the Grey, Puysegur and Milford coastal areas.
Watches for heavy rain and severe gales are now in force for parts of New Zealand.
