Jekyll and Hyde summer weather continues - scorcher forecast for Invercargill, rain and thunderstorms further north

Our crazy topsy-turvy summer continues this weekend - with scorching temperatures due in the deep south, heavy rain coming to the top of the south and more thunderstorms expected in the north.

Yesterday delivered lashings of summer warmth to the top of the North Island, with Auckland, Hamilton and Whangarei reaching 28C and Tauranga 25C.

It was cooler further south, and wet. Rotorua suffered flash flooding when 25mm of rain fell in an hour and 200 lightning strikes were recorded after a thunderstorm struck the city.

The downpour followed the flooding in Greymouth a day earlier, inundating homes and closed roads, and came just over a week after a deep low thrashed large swathes of the North Island, causing storm surges and flooding in South-East Auckland and Coromandel Peninsula.

A thunderstorm caused flash flooding in Rotorua yesterday. Photo / Ben Fraser / Rotorua Daily Post

Today, the Metservice says it's the top of the south's turn, with the hills behind popular camping spots near normally sun-drenched Motueka expecting between 100 and 120mm of rain in the 24 hours to noon.

There is moderate risk of thunderstorms this afternoon and evening in the top of the South Island.

A large chunk of the North Island, south of Waitomo, is also at risk of thunderstorms and downpours from this afternoon.

Exactly where will be most affected is not known, but the lower central North Island is considered most at risk of severe thunderstorms, downpours of 25mm to 40mm an hour and hail up to 15mm in diameter, the Government weather agency warned.

Meanwhile, Invercargill could be wilting in foehn-wind raised temperatures of up to 30C - making it only the sixth time in nearly 25 years that temperatures in our southern-most city had reached that high.

Foehn winds are caused when water-packed winds from the west lose their moisture over the mountains, an action that releases energy and warms the air up in the east.

The heat will be turned up today too - a high of 27C is forecast, a degree hotter than Auckland, 1200 kilometres to the north.

It's been a warm summer for Auckland, as shown by Miller, left, and London Crane last month. Photo / Doug Sherring

Central Otago will also enjoy a warm weekend, but temperatures won't heat up to the mid to high 20s in Dunedin and Christchurch until tomorrow.

Metservice meteorologist April Clark said a northerly flow meant the warm weather would also continue in the North Island.

But it may not be completely enjoyable.

"It's going to be quite muggy."

The weather could turn again later this week, although exactly what was coming was hard to forecast more than 48 hours out.

"It's looking like a low is forming from west of New Zealand and that could mean periods of rain for the North Island and rain for the West Coast of the South Island."