Warnings are in place for heavy rain and strong winds in parts of the south.
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The deluge is set to hit the Westland ranges and Fiordland from Tuesday morning, while severe gales are in store for the Canterbury High Country and Fiordland from Monday night.
Civil Defence Emergency Management says severe gale northerlies in the high country could gust to 130km/h in exposed places.
MetService had forecasted deteriorating weather, as a front arrives from the west.
The national forecaster's latest severe weather watch also indicates heavy rain is possible from 4pm Tuesday in Nelson west of Motueka, the Buller ranges, and the Canterbury headwaters north of Arthurs Pass.
There is also a watch in place for strong winds in central Otago, west of Alexandra, between 9pm Monday and 2pm Tuesday.
"Northerly winds may approach severe gale in exposed places during this time," MetService says.
NIWA forecaster Ben Noll told Newshub said there are some big "dirty" lows in the Tasman at present.
"Potentially we see the conditions become right for thunderstorms later this week."