Thursday, April 25, 2024

High and dry for many as we go into March

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Conditions are now ‘incredibly dry’ in parts of New Zealand, says WeatherWatch’s Phil Duncan.
NIWA forecasts indicate much of the region could enter the ‘dry’ category over the next 35 days.
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It is incredibly dry around parts of New Zealand as we end February and cross into March. Often there is no sudden change to our pattern at this time of year though the mornings are cooler, the dews heavier and the afternoons often still mild to hot. 

Conditions are now very dry and some regions are especially so: Marlborough, Wellington, Wairarapa, Hawke’s Bay (south of the Napier-Taupō Highway), Horowhenua and Manawatū, many parts of Northland, Auckland, Coromandel Peninsula and Bay of Plenty (although BoP may have some pockets of relief just in the days before we print this). 

Then we have Nelson, parts of Canterbury and into Central Otago. Twelve months ago only Nelson, Blenheim and Christchurch/Rangiora were in this very dry state and of course the North Island was saturated from Cyclone Gabrielle, the Auckland floods and other rain events.

NZ’s very dry end to summer is thanks to El Niño, which took a while to get going but has been in place all summer. 

People in the South Island and lower North Island have been increasingly telling us the windy weather has really been a theme. This windy weather is a classic sign of El Niño with high pressure parked a lot over southern Australia and to NZ’s north – and this encourages plenty of westerly winds. 

Also, high pressure is crossing NZ with dry weather. When highs arrive they usually bring in a cooler southerly flow (we saw frosts around Central Otago on Wednesday last week). When the highs move out to NZ’s east we then get a time with hotter nor’westers and sub-tropical airflows. 

Temperature-wise, Southland and Coastal Otago have been cooler this summer – along with Victoria and Tasmania in Aussie also receiving these injections of Southern Ocean airflows from time to time with passing cold fronts. 

The angle of these fronts means the Southern Alps and the ranges of the upper South Island and lower/eastern North Island limit how much rain can go east and north. With so much high pressure to the north of the country, that is keeping calmer, drier and often settled weather for the top half of the North Island.

The big dry hot summer we and others warned about last year is now here – and because El Niño and autumn share similar weather (that is, windier westerlies) it tends to make autumn more autumn-like. A hat on a hat, as we said back in spring. 

Our March ClimateWatch outlook is issued this Friday at RuralWeather.co.nz and we’ll have more details about how that month is shaping up in the first Farmers Weekly of March next week.

Comparing this time a year ago (late February ’23) with current conditions (late February ’24) shows soil moisture deficits across the country are much more severe this year. Map: Niwa

Upcoming Highlights:

• Monday is fairly dry but a few showers in the north of NZ, and a weak front approaches the south

• Tuesday and Wednesday sees that cold front move up the east of NZ towards Hawke’s Bay – totals aren’t huge

• Wednesday and Thursday sees high pressure then move back in briefly

• Showers and patchy rain possible from the west for the weekend

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