NIWA’s climate outlook for the February quarter indicated heavy rainfall, possible flooding, and warned of continued preparedness for extreme weather impacts.
La Niña continued during January, but gradually weakened. It will continue to affect Aotearoa New Zealand’s atmospheric patterns in coming months, even as neutral conditions were expected in early autumn.
Temperatures were forecast to very likely be above average (65% chance). More winds of tropical-origin and above average coastal SSTs would likely result in above average overnight temperatures and higher humidity, but increased cloudiness may lead to cooler daytime temperatures.
Rainfall totals were most likely to be above normal (45% chance). Sub-tropical low pressure systems and/or atmospheric rivers were forecast to occasionally impact the region, increasing the risk for heavy rainfall and flooding.
Soil moisture levels were equally likely to be near normal or above normal (45% chance each) while river flows were most likely to be above normal (50% chance).
Coastal sea surface temperatures (SSTs) ranged from 0.7˚C to 3.2˚C above average during January and a Tasman Sea marine heatwave reached record levels along the coastal western South Island.
Air pressure was forecast to be higher than normal over and to the south of the South Island and lower than normal north of the country. This was expected to be associated with an easterly quarter air flow anomaly for the season as a whole.
Rainfall was most likely to be above normal in the north and east of the North Island, near normal in the east of the South Island, equally likely to be near normal or above normal in the west of the North Island and north of the South Island, and equally likely to be near normal or below normal in the west of the South Island.
The rainfall outlook indicated heavy rainfall and possible flooding was possible. Therefore, continued preparedness for extreme weather impacts in the weeks and months ahead for the North Island and northern South Island was warranted. Dry conditions in the lower South Island may persist.
Sub-tropical air masses, in conjunction with marine heatwave conditions, may elevate overnight temperatures and humidity while also delaying the typical transition to cooler temperatures for much of the country.
The risk for tropical cyclones in the Southwest Pacific may increase during mid-to-late February. The effects from these storms as they decay and approach the country can cause flooding rainfall, strong winds, and coastal hazards.
