Kiwis had to wrap up warm on Wednesday morning as New Zealand faced an intense cold snap, preceding a front expected to move over the country from Thursday.
"Kia ora New Zealand, it's a chilly start to the day, especially across the South Island this morning," MetService said on Wednesday.
"Coldest spots were in towards Tekapo where the temperature dropped to -7C."
For Thursday, MetService expected heavy rain to start affecting New Zealand "in what looks like an extended period of unsettled weather".
"There's also risk of thunderstorms for the upper half of the North Island" including Auckland, said the forecaster.
MetService has issued heavy rain watches in six areas from Te Tai Tokerau in the north to Fiordland in the south.
The forecaster's severe weather outlook said a "complex trough" should cross the North Island onto the upper South on Friday, preceded by rain and strong northeast winds for many parts of the country.
"There is moderate confidence of warning amounts of rain for Bay of Plenty, northern Gisborne/Tairawhiti and western Tasman. Low confidence of warning amounts of rain extends over Coromandel Peninsula, the remainder of Tasman/Nelson and northern Marlborough, also from northern Fiordland into the Westland District, and over Dunedin and north Otago."
NIWA said the severe weather was the result of "two disturbances in the Tasman Sea" dragging tropical moisture into New Zealand.
"The combined system will produce rounds of heavy rainfall, particularly in the northern and eastern South Island, possibly swirling in the Tasman for up to a week!
"Right now, the heaviest falls are favouring Nelson-Tasman, north Otago and south Canterbury, though details will become clearer in the days ahead.
"Rounds of rain, some heavy, will likely be interspersed with sun during the week June 17 due to the slow-moving nature of the low."
Heavy rain watches
Northland
Period: 22hrs from 1pm Thu, 13 Jun - 11am Fri, 14 Jun
Forecast: Periods of heavy rain, and amounts may approach warning criteria. Thunderstorms with bursts of heavy rain are possible. Moderate chance of upgrading to a Warning.
Auckland including Great Barrier Island and Coromandel Peninsula
Period: 20hrs from 8pm Thu, 13 Jun - 4pm Fri, 14 Jun
Forecast: Periods of heavy rain, and amounts may approach warning criteria. Thunderstorms with bursts of heavy rain are possible. Low chance of upgrading to a Warning.
Mt Taranaki
Period: 20hrs from 10pm Thu, 13 Jun - 6pm Fri, 14 Jun
Forecast: Periods of heavy rain, and amounts may approach warning criteria. Moderate chance of upgrading to a Warning.
Bay of Plenty and Rotorua
Period: 22hrs from 10pm Thu, 13 Jun - 8pm Fri, 14 Jun
Forecast: Periods of heavy rain, and amounts may approach warning criteria. Thunderstorms with bursts of heavy rain are possible. Moderate chance of upgrading to a Warning.
Tasman northwest of Motueka
Period: 24hrs from 6pm Thu, 13 Jun - 6pm Fri, 14 Jun
Forecast: Periods of heavy rain, and amounts may approach warning criteria. Moderate chance of upgrading to a Warning.
Fiordland north of Doubtful Sound and the ranges of the Westland District
Period: 16hrs from 11am Thu, 13 Jun - 3am Fri, 14 Jun
Forecast: Periods of heavy rain, and amounts may approach warning criteria. Low chance of upgrading to a Warning.
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