MetService has issued three warnings and a watch for the South Island, covering heavy rain, snow and strong winds.

An Orange Heavy Rain Warning is in force for the Kaikōura Coast and Ranges and the north Canterbury ranges east of Lake Sumner.

It runs for 25 hours from 10pm Sunday 19 April until 11pm Monday 20 April.

MetService is forecasting 100 to 130 millimetres of rain in the warning area, with 150 to 200 millimetres expected for the Seaward Kaikōura Range.

Peak rates of 20 to 30 millimetres an hour are forecast on Monday morning, and the freezing level is expected to lower to between 1200 and 1400 metres.

MetService says there is a moderate chance of the warning being upgraded to red.

Streams and rivers may rise rapidly, with surface flooding, slips and difficult driving conditions possible. Its advice is to clear drains and gutters, avoid low lying areas, and drive cautiously.

MetService has also issued two Road Snowfall Warnings.

On Porters Pass (SH73), a 13 hour warning runs from 7pm Monday until 8am Tuesday.

Snow in showers is expected to lower to 800 metres on Monday evening, with 2 to 3 centimetres forecast to accumulate on the road from Monday evening to Tuesday morning.

On Lewis Pass (SH7), a 14 hour warning runs from 4pm Monday until 6am Tuesday.

Rain is expected to turn to snow about the summit on Monday afternoon, lowering to 800 metres in the evening.

Peak snowfall is forecast on Monday evening, with 3 to 5 centimetres possible about and south of the summit before conditions ease early Tuesday morning.

A Strong Wind Watch is also in place for Buller, Grey and Westland, covering 24 hours from 9am Monday until 9am Tuesday. MetService says southeast winds may approach severe gale in exposed places, with a moderate chance of an upgrade to a warning.

The heavy rain warning is next due to be updated at 10am Monday. The snowfall warnings and wind watch are next due to be updated at 11am Monday.