Why warm air from Australia means soaring weekend temperatures for many
Thursday, 31 October 2019
Many parts of the country are expected to bask in warm sunshine with light winds and soaring temperatures this weekend.
Some places in the east and inland are forecast to top 30 degrees Celsius, although right at the coast conditions may not be quite so balmy.
It's possible November temperature records could be set in some places, although the top November temperature ever recorded in New Zealand could be out of reach.
MetService meteorologist Peter Little said the warm air originated from Australia and was being transported across the Tasman Sea around the edges of a large, slow-moving high.
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How warm will it get?
Blenheim is forecast to get to 31 degrees Celsius on Sunday and 30C on Monday, for Hastings it's 31C and 29C on the two days, for Christchurch 31C and 28C, while Tauranga and Tokoroa are looking at 27C on both days.
Near the bottom of the South Island the warmest days are Saturday and Sunday, with Alexandra forecast to get to 30C and 29C, and even Invercargill is on course for a 24C Saturday and 23C Sunday.
Things are looking far more average in Auckland, with highs of 18C, 20C and 21C from Saturday through to Monday, while Wellingtonians have highs of 17C, 21C and 19C to look forward to.
So maybe not beach weather?
Little said Christchurch was a good example. Places in the very west of the city could possibly see temperatures around 30C. 'But for those heading for the beach it could be potentially 10C cooler.'
With sea temperatures around the country still fairly cold, as the land heated up and colder air flowed inland from the sea there would be a big contrast, which meant sea breezes could tend to be strong.
'It's possible some places right on the coast, if they have a westerly breeze, they will be very hot but there's also a chance there could be quite a big difference standing at the beach from 5-10km inland,' Little said.
Why will the warm Australian air get to us?
'It's basically coming down in a northwesterly,' Little said. The warm air would move over the bottom of the South Island and then scoot up over the country.
Because the high in the Tasman Sea was slow moving, it meant the warm air would be carried across from Australia for a prolonged period. 'Because the high isn't moving much, the pattern is able to keep going. We're still seeing the air being transported basically for about a three-day period.' Little said.
Niwa forecaster Ben Noll pointed out Australia was experiencing long-term drought conditions.
So is it all down to Australia?
No. Little said the already warm wind blowing from the west across New Zealand would not be strong, so it would have a chance to warm further as it crossed the country. For places east of high ranges and mountains, the air would warm even further as it descended on the eastern side of the ranges.
'Basically it's not a strong wind that's going to mix up a lot of colder air higher up in the atmosphere. It has a chance to really warm near the surface,' Little said.
Is it a record breaker?
Well, Noll said the overall November record for New Zealand of 35.6C recorded at Caterbury's Lake Coleridge in 1920 would be a 'big reach'. 'We're probably not going to see that,' he said.
But record or near-record November temperatures were possible for some locations in both islands. 'Temperatures of 33-34C are not out of the question for a location or two but it won't be widespread,' Noll said.
The second warmest November temperature was 34.8C recorded at Gisborne in 2016.
How long will the warmth stay around?
MetService said the settled, warm weather was expected to linger over northern and central New Zealand into the middle of next week, but for much of the South Island it looks as if Monday will be the last of the warm days in this spell.
Noll said high temperatures were likely to persist for the first 10 days of November.
'During the second week of the month and continuing into mid November, some strong fronts are possible in the South Island, bringing rounds of heavy rain and an increased risk for areas of flooding, especially in the west.'