MetService is forecasting widespread severe weather as an intense trough of low pressure closes in from the west.

The weekend just gone was hardly a calm start to meteorological autumn, with a series of fronts bringing areas of rain with heavy falls to both islands, as well as strong winds and fluctuating temperatures.

The trough reached the South Island on Sundayn night, and is moving eastwards across New Zealand during Monday.

Heavy rain is expected for the western South Island as the trough passes, as well as the already sodden central North Island.

Orange Heavy Rain Warnings are in place for parts of Fiordland, the Otago headwaters, the Tararua Range and Mount Taranaki.

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 Tairawhiti. 

Widespread strong or gale northwesterly winds also accompany the trough, easing in the south on Monday morning as the trough moves away, but affecting central areas until Tuesday afternoon.

A Strong Wind Warning is in effect for the Canterbury High Country with gusts expected to reach 120km per hour 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 per hour in exposed places.

"Stay up to date with the latest forecasts on metservice.com as the situation develops. More Warning areas could be added further north, and existing Watches could be upgraded as we gather more information," says MetService meteorologist Ngaire Wotherspoon.

Strong, cold southwesterly winds follow the trough, spreading heavy showers with embedded thunderstorms over southern and central New Zealand.

This unseasonable cold change will be felt across the country at the beginning of the week, and snow could settle above 1000 metres in Fiordland and the ranges of Otago on Monday.

“Hot temperatures occurred in eastern South Island areas over the weekend, so this cold southerly change will be felt keenly over the next couple of days," says Ngaire.

"Alexandra had a high of 29°C on Saturday, and by Tuesday they have a forecast high of 14°C, and 4°C overnight.”

The strong southwesterlies are likely to generate large swell along the south and west coasts later in the day on Monday, before easing on afternoon Tuesday as the trough moves away.

A Heavy Swell Warning has been issued for Otaki to Cape Terawhiti with northwest combined waves rising to 3.5 – 4 meters from Tuesday 1am until 1pm.  

“An end to the wild weather is on the horizon; a ridge of high pressure settles over most of the country on Wednesday, bringing calmer, clearer conditions,” says Ngaire.