“Heavy rain is expected and amounts are likely to exceed warning criteria,” MetService said, adding there was a “high chance” the warning would be upgraded.
MetService meteorologist Dom Barry said a series of weak fronts would be tracking up the South Island from Wednesday and more watches or warnings for other areas were likely to be issued.
Barry said some parts of the West Coast would “easily” see half a metre of rain at higher elevations in the next 10 days or less.
“There most certainly is going to be heavy rain at sea level,” he said.
Barry said the wettest days for the country looked to be Wednesday and Thursday, with western and southern areas of the South Island in the firing line.
The “warm and moist” northwesterlies developing over the South Island would also bring warmer temperatures, Barry said, with eastern parts of the country set to see higher-than-average minimum and maximum temperatures later this week.
“For the easternmost places like Christchurch, Oamaru, Napier and Hastings, maximums in the mid-20s can be expected. Overnight temperatures will stay warm as well, in some cases only being a couple of degrees cooler than the day’s maximum, which might make sleeping a struggle for some,” Barry said.
MetService predicts highs of 26C to 27C in Hawke’s Bay on Thursday and Friday – Hawke’s Bay Anniversary day – and lows of 13C and 16C.
However, rain and wind are set to return elsewhere, bringing gloomy conditions for parts over the long weekend.
“Low pressure is returning at the end of this week, meaning some wetter weather is in store over the long weekend. With some drier weather possible for Labour Day, it is worth checking the forecast to get the best out of the weekend,” Barry said.
MetService said a large trough of low pressure was likely to cover much of New Zealand on Saturday, with northerlies affecting the North Island and southerlies developing over the South Island.
“There’s considerable uncertainty regarding the areas most affected, however, heavy rain could affect many parts of the country.
“Consequently, there is low confidence that heavy northerly rain could reach warning criteria about eastern Bay of Plenty, Waitomo, Taumarunui, Taranaki, Kāpiti [including the Tararua range], Wellington, Marlborough, Nelson/Tasman and northern Buller.
“There is also low confidence that heavy south or southeasterly rain could affect eastern parts of the South Island from eastern Marlborough to Clutha.”
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