MetService has issued a Severe Weather Outlook for the week ahead, with heavy rain expected for the west of the South Island and lower North Island.

A front is slow-moving over the northwest of the South Island from Saturday night through to late this afternoon, Sunday December 17.

A moist northwest flow ahead of this front is bringing periods of heavy rain to western areas of the South Island and the Tararua Range. Heavy Rain Watches and Warnings are in force.

Monday December 18
Fronts over the centre of the country are expected to weaken during Monday as a high expands over the South Island.

MetService says some lingering heavy rain is possible about the Tararua Range early in the day, but it is unlikely this will require a warning.

Tuesday December 19
The high slowly moves north during Tuesday and no severe weather is expected.

Wednesday December 20
On Wednesday, the high remains over most of the country, but a front approaching from the west is expected to bring rain to Fiordland and strengthening northwest winds across the South Island.

There is low confidence that a heavy rainfall warning will be needed for Fiordland.

For inland areas of Marlborough, Canterbury and Otago, there is low confidence that winds will be strong enough to require a warning.

Thursday December 21
On Thursday, the front should move up the South Island, followed by another high.

The rain and wind should ease and there is minimal risk of severe weather.