MetService is warning parts of the country to expect gale northwesterlies and heavy rain as an intense trough of low pressure moves over the motu overnight on Sunday and into Monday.

It has issued orange rain warnings overnight until Monday morning for:

Fiordland north of Doubtful Sound, the Otago headwaters, the Tararua Range and Mt Taranaki.

A burst of possibly heavy rain is also predicted for parts of Auckland between 3 and 5pm Sunday.

Already this weekend there has been heavy rain in parts of both the North and South islands, as well as strong winds and fluctuating temperatures.

Heavy rain watches are in place for the Westland ranges, the headwaters of Canterbury lakes and rivers from Arthurs Pass southwards, central and western areas of the North Island and the ranges of eastern Bay of Plenty and Tairāwhiti.

The trough will be accompanied by widespread strong or gale northwesterly winds, which will ease in the south on Monday morning but affect central areas until Tuesday afternoon.

A strong wind warning is in effect for the Canterbury high country with gusts expected to reach 120km/h in exposed places.

Strong wind watches are in force for Fiordland, inland Southland and Otago, and central and southern parts of the North Island, gusting 100 km/h in exposed places.

More warning areas could be added as the trough moves north, and existing watches could be upgraded.