The solar blow torch is firmly directed on the south of the country with temperatures expected to soar to a scorching 35C.

In the north sweltering humidity, that saw temperatures barely fall under 20C overnight, is turning to yet another day of violent thunderstorms for central regions.

Already the mercury has skyrocketed to 31C at Dunedin Airport by lunchtime with many other places in mid to high 20s.

A Weatherwatch spokesman said the heatwave could see highs exceeding 35C in the southern half of the South Island through some valleys.

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Metservice said earlier Alexandra is on target to being the hottest place in New Zealand today with the mercury expected to hit 33C but Invercargill, which broke a century-old record yesterday when it hit 32.3C, is due for another sizzling day.

With 32C forecast MetService says today has all the same ingredients for a hot day and there was a possibility a new record could be created within 24 hours.

Just after 10.30am Invercargill was already 27.4C, the hottest place anywhere in New Zealand. At midday it was 29.2C and Niwa said it was already tracking warmer than Sunday's record-shattering day.

Temperatures are expected to reach 30C and higher across other parts of Southland and central Otago with Gore to hit 31C and Wanaka 30C.

HOT HOT TEMPERATURES for the South. A warm northeasterly wind flow over the New Zealand, combined with the heat from...

Posted by MetService New Zealand on Saturday, 13 January 2018

Meanwhile a thunderstorm watch has been issued for violent storms to rock the central North Island after lunch as warm, humid conditions and light winds combine to produce towering thunder-charged clouds.

MetService says the main risk of storms today is about southern and eastern Taupo, Taihape, inland and southern Taranaki, Whanganui, Manawatu and the western ranges of
Hawke's Bay.

The forecaster said the thunderstorms, which were expected to strike between about 3pm and 10pm, could be severe with torrential downpours and small hail.

It warned localised deluges could lead to flash flooding and prove hazardous to those on the roads. Streams and rivers and narrow valleys were at risk of suddenly becoming inundated, with the threat of slips.

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The thunderstorms were expected to die away late this evening.

Yesterday nearly 2000 bolts of lightning were recorded across the central North Island ranges as storms hit throughout the afternoon and evening.

Everything is about to go downhill rapidly tomorrow night as another storm approaches the country.
Rain and strong winds are set to hit the country midweek with a swathe of wind and rain warnings expected to be issued in the coming day.

The first heavy rain watch has been issued for Nelson and the Westland ranges south of Otira with rain due to hit from midnight Wednesday and lasting for nearly 24 hours.

Weatherwatch.co.nz said the low in the Tasman Sea would roar into life over the next 24 hours before falling apart as it moved on to the country mid-week.

Head analyst Philip Duncan said the low would peak in intensity tomorrow when it hadn't reached land but it would still bring wind, rain and showers across New Zealand.

He said the low would encourage more of the hot, humid airflow from the sub-tropics fuelling the heatwave in the lower South Island today and tomorrow with sweltering 35C highs possible in central Otago.