Warm, wet summer days ahead
La Nina settles in for northern NZ over next three months
Plenty of warm and wet days lie ahead for northern New Zealand this summer, with the classic flavours of a La Nina climate system coming through strongly in Niwa’s new outlook.
“Marine heatwave” conditions that have also formed in the north could widen to other coastal areas over the next three months, bringing their own influences to our summer weather.
Caused by a build-up of coolerthan-normal waters in the tropical Pacific, La Nina traditionally brings warmth everywhere in New Zealand over summer — but with stark differences in regional weather patterns.
As more northeasterly winds arrive, rainy weather becomes a pattern over the North Island’s northeast, while drier conditions tend to dominate the South Island’s south and southeast.
Niwa yesterday reported that, consistent with “moderate” La Nina conditions, air pressure was forecast to be higher than normal over and to the southeast of the South Island, and lower than normal to the northwest of New Zealand.
That was expected to associated with northeasterly flow anomalies.
Although patterns of higher than normal pressure and drier conditions were expected to start summer, moist, subtropical disturbances were expected to reach the country occasionally, particularly the North Island and northern South Island.
These systems could cause areas of heavy rainfall and flooding.
Niwa also reported that marine heatwave conditions formed near the northern North Island and northern Tasman Sea during November. That would spell the third marine heatwave in four years — with implications for everything from hotter temperatures on land to further glacier melt in the Southern Alps.
The outlook predicted air temperatures were “very likely” to be above average in all regions and with sometimes elevated humidity levels, particularly in the North Island.
Rainfall levels were likely to be near normal or below normal in the east and west of the South Island — and equally likely to be near normal or above normal in all remaining regions.
There was also a slightly elevated risk of tropical cyclones for New Zealand — typically, an average of one ex-system swept within 550km each season. be air