A front is forecast to move across the east of the North Island early on Tuesday, says a MetService spokesperson. 

"There is low confidence that rainfall accumulations will meet warning criteria over eastern Bay of Plenty and the western ranges of Gisborne.

"On Tuesday, over the lower South Island, there is low confidence that westerly gales could become severe."

The MetService says the winds should ease for a time on Wednesday, as a weak ridge of high pressure moves across New Zealand from the west.

"But on Thursday gales are again expected, with low confidence of severe gales first from the northwest then west to southwest.

"On Thursday there is also moderate confidence of significant heavy rain over Fiordland, Westland and the Otago and Canterbury headwaters, easing to low confidence on Friday."

Severe Weather Watch for South Island

Heavy rain is expected for the west of the South Island during Sunday and Monday. Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

"An active front moves northwards over the South Island during Sunday and Monday," says a MetService spokesperson.

"This brings heavy rain, and Watches and Warnings are in place."

People are advised to keep up to date with the latest forecasts in case changes are made.

Heavy Rain Watch is in place for:
Area: Tasman west of Motueka, the Bryant and Richmond ranges including the Rai Valley
Valid: 9 hours from 6:00am Mon 11 Sep to 3:00pm Mon 11 Sep
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria, especially about the ranges.

Area: Westland north of Otira, and Buller
Valid: 10 hours from 1:00am Mon 11 Sep to 11:00am Mon 11 Sep
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria, especially about the ranges.

Area: Fiordland
Valid: 5 hours from 9:00am Sun 10 Sep to 2:00pm Sun 10 Sep
Forecast: A period of heavy rain is expected, and rainfall accumulations may approach warning criteria, especially about northern Fiordland.

Area: Headwaters of the Otago Lakes and Rivers
Valid: 8 hours from 10:00am Sun 10 Sep to 6:00pm Sun 10 Sep
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria within 15 km east of the main divide.

A Heavy Rain Warning is in place for the headwaters of the Canterbury Lakes and Rivers about and south of Arthur's Pass. This is valid for 19 hours from 1pm Sunday, September 10 to 8am Monday, September 11.

"Expect 140 to 180 mm of rain about the main divide, and 70 to 110 mm within 15 km further east. Peak rates of 10 to 20 mm per hour expected about the divide. Freezing level about 2200 metres."