Heavy rain is forecast for western areas on Sunday and Monday, with strong gale-force southwesterly winds expected over New Zealand by Monday.
Temperatures were also set to plummet following the end of the long weekend, with snow lowering to 800 metres over southern areas of New Zealand.
"The culprit is a deep trough of low pressure, which moves across the country from the Tasman Sea on Sunday and Monday," MetService meteorologist Peter Little said.
"The trough is preceded by a moist northerly flow, which will bring a period of rain to western parts of the country, and northerly gales to exposed places.
"The heaviest rain is likely in the west of the South Island, and a warning may be issued in the coming days."
After the trough, a strong, cold and wet southwesterly flow would spread over New Zealand.
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In the far south, temperatures might only reach maximums of 11C or 12C. Bursts of hail could be expected too.
While tropical cyclone Harold was expected to pass well away from New Zealand, it had caused a lot of damage to Vanuatu, Fiji and Tonga.