Ex-tropical cyclone Uesi is expected to continue hammering western areas of the South Island on Monday.
A total of 100-150 millimeters of rain is forecast to hit by Monday morning, and there may be a chance of flooding or slips on the West Coast, WeatherWatch says.
Northern areas near Westport are due to receive most of the rain, and coastal regions in Westland may see some light rain or showers.
The prolonged rain is expected to last until at least Wednesday morning.
There will be noticeable gusts too, with exposed mountain areas near the Southern Alps forecast for winds over 110 km/h. Exposed coastal districts may see gusts exceeding 90 km/h.
The gale-force winds are set to weaken on Tuesday, with maximum gusts forecast to be 70 km/h.
The warmer northerly winds from ex-tropical cyclone Uesi flowing over the Alps will see Christchurch reach temperatures in the low 30s on Monday.
WeatherWatch is also forecasting that another tropical cyclone is likely to appear next week, this time for the northeast of New Zealand.
"The storm could be a tropical cyclone until the end of the week, with it developing in the Samoa/Niue area and tracking southeastwards towards the Cook Island region before high pressure turns it more southwards late week," WeatherWatch said in a statement.
It is currently not forecast to hit New Zealand.