A ridge of high pressure is expected to extend over northern New Zealand during Monday and Tuesday.

Meanwhile, a strong northwest flow is forecast to develop over southern and central New Zealand during Monday and strengthen further on Tuesday ahead of an approaching front. This front should move onto the deep south overnight Tuesday and cross the South Island and lower North Island during Wednesday.

A period of heavy rain is expected about Fiordland and the ranges of Westland during Tuesday and early Wednesday, with a high confidence of rainfall amounts reaching warning criteria south of the Glaciers and lower confidence further north.

North to northwest gales are expected to develop ahead of the front affecting Fiordland from late Monday and exposed inland parts of the South Island from Southland up to Marlborough on Tuesday and early Wednesday, as well as about Wellington, Wairarapa and southern parts of Hawkes Bay.

There is a generally low risk of these winds briefly reaching severe gale during this time. However, this risk is considered moderate about and east of the Main Divide from Mt Cook southwards, including the Southern Lakes, on Tuesday.