A scorching summer is expected across the country from next month as temperatures rise due to La Niña.
The National Institute of Water and Atmospheric Research (NIWA) has issued a La Niña alert - in which ocean surface temperatures periodically cool in the equatorial Pacific - during October.
NIWA said in a media release on Friday that temperatures are “very likely to be above average” across the country, with a period of “particularly warm conditions from around the second week of November” to next January.
It follows an increase in New Zealand’s coastal sea surface temperatures (SSTs) between 0.5˚C to 1.0˚C above average this month.
SSTs are expected to become “more unusually warm over the coming month or two”, which could lead to marine heatwave conditions in some regions, according to NIWA.
Temperatures across the North Island, Taranaki, Whanganui, Manawatū and Wellington are very likely to be above average at 65 per cent chance, according to NIWA.
Temperatures in Gisborne, Hawke’s Bay and the Wairarapa are very likely to be above average at 60 per cent chance.
The West Coast, alps and foothills, inland Otago and Southland, meanwhile, are very likely to be above average at 70 per cent.
Coastal Canterbury and east Otago's will be much like the North Island, with temperatures very likely to be above average at 65 per cent.
In addition, higher than normal air pressure over the South Island, as well as the south and east of the country, is expected to increase the chance for dry spells in the South Island and western North Island in particular.
Rainfall totals across the North Island are equally likely to be near normal at around 40 per cent chance, or below normal at 35 per cent.
Rainfall totals in Gisborne, the Hawke’s Bay and the Wairarapa are most likely to be near normal at 40 per cent chance. However, moist, humid easterly winds will increase the chance for periodic heavy rainfall across Gisborne and the northern Hawke’s Bay, although chances are lower in southern areas like the Wairarapa.
Rainfall totals across the West Coast, alps and foothills, inland Otago and Southland are most likely to be below normal at 50 per cent. However, the development of La Niña-like patterns may contribute to drier conditions in the coming months around the hydro lake areas.
Coastal Canterbury and east Otago’s rainfall totals are about equally likely to be below normal at 40 per cent or near normal at 35 per cent.
Meanwhile, the risk for a tropical cyclone passing by the country during the tropical cyclone season - between November 2021 and April 2022 - is also elevated, according to NIWA’s SW Pacific Tropical Cyclone Outlook.
On average, around one tropical cyclone passes near the country every year, bringing with it heavy rain, strong winds and rough seas.
“Rainfall is most likely to be below normal in the west of the South Island, near normal in the north and east of the North Island and about equally likely to be near normal or below normal in all other regions,” NIWA said.
“Occasional sub-tropical low pressure systems can bring heavy rainfall and possible flooding to New Zealand, particularly in the northern and eastern North Island.”
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