Magwala did not dismiss more alerts being issued as the day continued.
On its website, MetService urged people to take these alerts seriously, pointing out the risk for vulnerable people.
“Everyone is vulnerable to extreme heat. However, babies and infants, older people, those with pre-existing medical conditions or on certain medications are more at risk.
“International research shows that extreme heat and heatwaves can cause illness and death, but effective planning and actions can readily reduce its effects on health.”
Magwala said a low-pressure system over the Tasman Sea and warm wind being pushed on to the country were responsible for the high temperatures over coming days.
He said for eastern parts of both islands of the country there might be light showers which would make for a muggy afternoon.
Magwala advised even those wanting to beat the heat to enjoy at least a little time in the sun over the next few days before the weather turns later in the week.
MetService has upgraded a heavy rain watch in Tasman to a heavy rain warning from 9am to 2pm for Tasman and rain watches are in place for Buller, the Grey District and the Richmond Range and the Bryant Range.
Heavy rain warnings are in place for Westland and the Canterbury headwaters south of Arthurs Pass tomorrow, with a strong wind warning also issued for the Canterbury High Country, as gusts could reach 120km/h.
Elsewhere, a strong wind watch has been issued for Fiordland, with gusts reaching about 90km/h in exposed places. Heavy rain watches have been issued for Fiordland north of Doubtful Sound, the Otago headwaters and the Grey District.
As the country heats up, the temperatures were expected to combine with the wind to cause showers to develop in parts during the afternoon and evening.
MetService said there was a moderate risk of thunderstorms for southeast Waikato, inland Bay of Plenty including Rotorua, Taupō, inland and southern Hawke’s Bay, eastern Taihape and the east of Tararua District.
The thunderstorms could see bouts of intense heavy rain and small hail.
In many areas across the country, the UV is expected to climb to a “dangerous” level 10 on the index.
Magwala advised everyone to apply sunscreen and wear sunglasses today, even if it is overcast.