Magwala told the Herald early-morning temperatures would fall to single digits for parts of the lower South Island, as the cold front passes.
According to MetService, Invercargill is forecast to tumble down to 4C overnight on Wednesday, while Queenstown will fall to 8C.
In the North Island, a ridge of high-pressure over the Tasman Sea would mean plenty of fine and dry weather through the early part of the week.
“With sunny spells in many places. Good news for the cricket in Hamilton on Tuesday.”
Hamilton is forecast to peak at 24C today and tomorrow, before rising to 26C on Thursday.
Magwala said the ridge would bring settled weather for most of the North Island.
“But there will be some morning patchy cloud in the North Island,” he said.
Auckland is forecast to reach a high of 24C today before rising to 25C tomorrow and Thursday.
Tauranga will hit a high of 23C today and tomorrow and 25C on Thursday.
In Northland, Kaitāia will reach a high of 24C for the rest of the week, while Whangārei will reach 22C today and 23C tomorrow.
According to MetService, a low-pressure system passing northeast of the country may bring some cloud and occasional rain to Tairāwhiti Gisborne and northern Hawke’s Bay later in the week.
“But the chance of significant impacts remains very low.”
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