MetService has issued a Severe Weather Outlook for New Zealand for the coming week.

Strong west to northwest winds are forecast to affect parts of central and southern New Zealand, says a MetService spokesperson.

There is a west to northwest flow strengthening across New Zealand today ahead of a front approaching from the west.

"Strong winds are forecast to affect parts of central and southern New Zealand, and Strong Wind Watches are now in force for areas from Hawke's Bay down to Southland," says a MetService spokesperson.

"People are advised to keep up to date with the latest forecasts in case any watches are upgraded to warnings, or further areas are added."

MetService advises that a west to southwest flow will cover New Zealand on Monday and Tuesday, with an associated low confidence for warning amounts of rain in Fiordland, and low confidence for severe westerly gales in the south of Southland, including Stewart Island, and Clutha.

"On Wednesday, a large trough over the Tasman Sea with an embedded rain band moves north over the South Island, followed by a change to strong, cold southerlies.

"There is moderate confidence that there will be warning amounts of rain for Fiordland and Westland, and low confidence for warning amount of rain in Buller.

"Additionally, there is low confidence that northwest winds could rise to severe gale for a time about high country areas of Canterbury."

MetService says in eastern and southern areas of the South Island, a period of rain is expected from Wednesday into Thursday with snow lowering to about 400 metres.

"However, the duration and intensity of the rain may not be long or heavy enough to reach warning thresholds. However snow could significantly affect some roads and passes in the South Island."

On Thursday, the trough and associated rain is expected to move onto the North Island.

"But there is currently uncertainty with the distribution of rain and strongest winds, and MetService will monitor the situation.

"However, there is at least low confidence for the possibility of severe southerly gales affecting Wellington and northern and eastern Marlborough."

A Strong Wind Watch is in place for the following areas:

Area: Hawke's Bay south of State highway 5, the Tararua District, and Wairarapa about and north of Featherston
Valid: 13 hours from 9:00am Sun 16 Jul to 10:00pm Sun 16 Jul
Forecast: Westerly winds may approach severe gale in exposed places, especially inland towards the ranges.

Area: Canterbury High Country, and inland Marlborough south of Kekerengu
Valid: 12 hours from 12:00am Sun 16 Jul to 12:00pm Sun 16 Jul
Forecast: Northwest winds may approach severe gale in exposed places.

Area: Inland parts of Otago, Southland including Stewart Island, and Fiordland
Valid: 9 hours from 9:00pm Sat 15 Jul to 6:00am Sun 16 Jul
Forecast: Northwest winds may approach severe gale in exposed places, especially about higher ground.