MetService says that is expected to move to central New Zealand this afternoon and this evening, followed by a strong south to southwest flow.
Christchurch has a high of 19C and will get showers today. There is also a chance of heavy rain and thunder, as well as hail this afternoon.
Those in Dunedin are also forecast to see a lot of rain and a chance of thunder and hail later.
"Scattered heavy showers with hail and isolated thunderstorms are expected to spread onto southern and eastern parts of the South Island this morning and afternoon onto the lower North Island late this afternoon and early evening.
"There is a moderate risk of thunderstorms about much of Southland, Otago and South Canterbury late this morning and afternoon - and also about mid and north Canterbury, the Kaikoura area and Wairarapa this afternoon and early evening.
"A broad low risk covers other parts of the lower Northland, Marlborough, Canterbury, eastern Nelson down to southern Fiordland during the afternoon and evening.''
Those thunderstorms are forecast to bring heavy rain and strong gusts of up to 110km/h. Hail is expected to be between 5 to 15mm in diameter.
Aucklanders are in for a temperature high of 20C today.
There is the odd shower expected this morning. Otherwise, long fine spells are forecast in the City of Sails.
Hamilton and the Waikato region will see a mostly fine day as well, save for a chance of morning shower.
Further north, Whangarei is in for a 23C high and a mostly sunny day; while those in Kaitaia will enjoy fine spells this afternoon and a high of 22C.
It's a sunny day in Gisborne, but there are a few evening showers expected and a high of 25C and an overnight low of 10C.
New Plymouth will get fine spells throughout the day, but there are strong westerly winds in the area and an overnight low of 6C.
Napier also gets rain today - as does Palmerston North - and those in Wellington will have to be prepared for rain as there is a chance it will be heavy rainfall this afternoon.
TODAY'S FORECAST:
• Auckland: 20C high. Odd shower clears morning to long fine spells.
• Whangarei: 23C. Cloud clears to mostly sunny this morning.
• Napier: 26C. A fine day, evening showers.
• Wellington: 20C. Rain, chance heavy.
• Nelson: 21C. Mainly fine, chance evening shower.
• Christchurch: 19C. Showers, chance heavy/ thunder with hail.
• Queenstown: 14C. A few showers with hail.
• Dunedin: 13C. Showers, chance heavy/ thunder with hail.