After its wettest November on record and a damp start to December, Northland is set to be warm and humid but wet this summer as the La Niña weather pattern and a marine heatwave develop
around the country.

Niwa has released its climate summary for December to the end of February, and there’s some bad news in there for Northland, with the region likely to experience more rain than normal, and warm, humid conditions.

Niwa national climate centre meteorologist/forecaster Ben Noll said Northland has already had a wet start to summer, after its incredibly wet November, with tropical and sub-tropical weather systems expected to bring warm, humid and wet weather to the region over summer.

There were four Heavy Rain Watches issued for Northland last month, two of which were upgraded to Orange Heavy Rain Warnings, and there has already been one Heavy Rain Watch issued this month.

Whangārei Airport recorded 365mm of rain last month, well ahead of the previous November record of 257.6mm in 2000. It was also more than five times the November average of 71.5mm.

“One thing of interest so far is that while your daytime temperatures have not been particularly high, you’ve had some very warm, compared to normal, overnight temperatures up there. For Northland we are expecting this summer to be wetter than normal, with a 75 per cent chance that rainfall will be above or near normal levels. Low-pressure systems are forecast to drop down into the region with some regularity, which may increase the risk for occasional heavy rainfall,” Noll said.

There’s also a 70 per cent chance that temperatures are very likely to be above average.

“More sub-tropical winds and marine heatwave conditions will result in high heat and humidity at times. There may be similarities with last summer, though this summer is potentially going to be more humid with a warm, moist air flow coming from the tropics and sub-tropics.

“There will be some long, fine spells where people can enjoy the sun, but there’s also the likelihood of above average rainfall for the summer in Northland. That doesn’t mean it won’t be some hot days.”

Noll said La Niña is the culprit, bringing the weather pattern to Northland – warm seas that then put more moisture into the air, which means more rain and more humidity from the weather systems heading to the region.

He said it is too early to give an accurate forecast for Christmas, but at this stage it looks like there will be some unsettled weather leading up to it, but things may settle down for the Christmas weekend.

“There’s some indication that as we get to the week starting December 19 there will be some not-so-nice weather, but later in the week, around December 21/22, things will settle down and it could be a fairly nice Christmas. But we won’t know for sure until closer to the time,” Noll said.

La Niña continued during November and a marine heatwave developed in the country’s coastal waters with sea surface temperatures 1.1˚C to 1.7˚C above average. Both will influence the summer climate, Noll said.

More sub-tropical northeast winds may result in more frequent hot days – above 25˚C for inland and western parts of both islands. Conversely, a reduction in northwesterly “Foehn” winds will likely mean fewer hot days for eastern areas.

Warmer than average regional seas are expected to fuel occasional heavy rainfall events; however, during periods of high pressure, dry spells will occur, particularly about inland and western parts of both islands. A dry spell is possible from mid-December to early January.