La Niña brings hot and humid summers to New Zealand. It occurs every three to five years due to changes in ocean temperatures near the equator.
The combined effect of the warmth, humidity, and wet weather creates optimal growing conditions for pollen-producing weeds, grasses, shrubs, and trees, Asthma and Respiratory Foundation NZ chief executive Letitia Harding said.
People with asthma and allergies should ensure they have enough medication before medical practices close for Christmas, she said.
* Chance of dry November; La Niña could bring subtropical storms in summer to northern areas
* Change in climate could bring some decent rain – but not for a while yet
* Australia bushfires: Yellow Auckland sky could return but wind change will shift it
La Niña is creating similar challenges across the Tasman, with a wet spring leading to record levels of grass pollen.
The conditions have also seen the worst hay fever season in more than five years in Canberra, according to the Australian National University, which resulted in state-wide health warnings being issued.
NIWA meteorologist Ben Noll said La Niña is expected to influence a warmer than average, but wetter summer for the North Island and upper South Island.
“Spring has already recorded higher than average temperatures with October being 1.2 degrees Celsius above average across New Zealand,” he said.
“It’s likely that these conditions will continue to influence pollen counts as plants continue to thrive.”
Up to 80 per cent of asthma is associated with an allergy, with one in eight adults and one in seven children in New Zealand suffering from the illness.
With the borders closed, record numbers of Kiwis are likely to travel domestically during the upcoming summer holidays, Harding said.
“Travelling to different places will expose people to different asthma and allergy triggers that they may not be accustomed to,” she said.
“A summer break doesn’t mean an asthma medication break so don’t get caught out! It’s important to take your medication as prescribed, even if you don’t have symptoms.”
La Niña occurs when strong winds blow warm water at the ocean’s surface away from South America, across the Pacific Ocean towards Indonesia.
As this warm water moves west, cold water from the deep sea rises to the surface near South America.