A heavy rain watch is in place for the Bay of Plenty.

The MetService is forecasting periods of heavy rain, with rainfall amounts predicted to approach warning criteria, and "thunderstorms are possible".

Southwesterlies over the country ease during Tuesday as a ridge of high pressure moves onto New Zealand from the Tasman Sea, says the MetService.

"The ridge then moves over the North Island on Wednesday with a northwesterly flow developing over the South Island.

"On Thursday, a front is expected to move north across the country from the southwest, bringing a brief period of heavy rain to the west coast of the South Island. It is followed by cold southwesterly winds.

"There is low confidence that rainfall accumulations could reach short-duration warning criteria in Fiordland during Thursday."