Weather: 'Coastal inundation', heavy rain warnings for South Island

The South Island is at risk from heavy rain, severe gales and coastal inundation on Tuesday as the first of a series of fronts and troughs begin to affect New Zealand.

"The effects of this weather could be significant," MetService says.

"We have issued a number of severe weather watches and orange warnings for heavy rain and severe gales around Aotearoa ahead of the oncoming rain band."

The heaviest falls are expected on the South Island's west coast. Heavy rain is possible from 4pm Tuesday in Nelson west of Motueka, the Buller ranges, the Otago headwaters and the Canterbury headwaters north and south of Arthurs Pass.

As well as rain, there will be strong winds. Civil Defence Canterbury has issued a warning until 7pm on Tuesday for severe north to northwest gales gusting 120 km/h in exposed places.

"The strongest winds expected near the Southern Alps on Tuesday, with strong wind warnings and watches already in place for some areas," MetService warns.

"The combination of heavy rain, strong winds at high tide, along with low air pressure could cause some coastal inundation for low-lying areas of Nelson, Buller, and Westland overnight Tuesday into Wednesday."

There's more bad news after this as a "complex and slow-moving low-pressure system" moves in on Wednesday through to Friday.

"It will drive in some big waves on the western side of both islands too with dangerous marine conditions for a time late this week," WeatherWatch warns.

"[There's] more snow for the Southern Alps and most ski fields too with a late-week southerly change."

Newshub.