La Nina is coming and it's bringing a hot, dry summer

Wednesday, 6 December 2017

Robbie Cookson 18, and Madi Fulton Buckle 17 of Nelson enjoy the waters off Rocks Road in Nelson during the scorching Summer weather.

Break out the barbecue and take out your togs if you haven't already, because summer is shaping up to be a scorcher.

Nelson's temperatures have gone above 20 degrees Celsius for 12 days running, and show no signs of cooling off, according to Metservice forecasts.

Niwa meteorologist Seth Carrier said this weather is thanks to a La Niña-like weather pattern, which brings warm sea-surface temperatures, as well as high-pressure and low rainfall to the South Island in particular.

Sea surface temperatures are up to 6 degrees warmer in some places, and are generally 3 degrees warmer around New Zealand, thanks to La Nina weather patterns.

Carrier said it was too early to tell if this summer was likely to be a record-breaker, but their seasonal forecast suggests that Nelson is very likely to have a drier and warmer than average summer.

Sea-surface temperatures around the South Island are on average 1-3 degrees above normal, with some pockets off the West Coast reaching as high as 6 degrees warmer than normal.

Robbie Cookson, 18, and Madi Fulton Buckle, 17, of Nelson take advantage of the warm sea temperatures at the beach off Rocks Road.

Carrier said 'sea surface temperatures were quite anomalously warm for this time of year'.

'Being an island country, the surrounding water temperatures have a very large effect on New Zealand's weather, that's one of the reasons temperatures have been so warm recently,' he said.

The hot sea is keeping temperatures up, while the high pressure associated with La Niña keeps rainfall low.

'The primary reason we've has some quite dry weather recently is we're becoming more of a La Niña pattern, which has certainly been the case for the last three or four weeks at least.'

Nelson had 25mm of rainfall last month, just a third of the usual 78mm.

'Early 2017 was actually quite wet for a lot of places in NZ, so this dry trend is a quite recent thing,' he said.

Carrier said generally El Niño and La Niña don't follow a regular pattern. On average they tend to happen every three to seven years, but 'that's not set in stone'.

He said that the weather now was 'right at the brink' of what would be considered an official La Niña, and New Zealand was experiencing 'significant' weather effects associated with La Niña.

The Tasman District Council (TDC) Dry Weather Taskforce had its first meeting of the summer last Tuesday.

The taskforce convenor, Dennis Bush-King, said that Stage One water restrictions for users on the Waimea Plains will come into force from next Monday.

'At last week's first meeting the Dry Weather Task Force noted that it was likely restrictions would have to be put in place within a week.

'As predicted, the Waimea River has dropped down to trigger levels at Wairoa Gorge so we are moving to Stage 1 rationing for urban users and most other water users on the Waimea Plains,' he said.

At this stage of rationing, watering restrictions are in place in Richmond, Mapua, Ruby Bay, Brightwater, Wakefield, and Hope, with only handheld watering allowed on every second day.

Consented water take levels will be cut by 20 per cent in the Upper Catchment, Reservoir, Waimea West, Delta, Golden Hills, and the Upper Confined Aquifer zones on the Waimea Plains.

Nelson City Council's acting group manager of infrastructure Shane Davies said the council was monitoring water levels at the Roding and Matai supplies.

'There are currently good water storage levels in the Matai dam, and we'll keep people informed if there's any cause for concern,' he said.

Davies said the Council encouraged people to use water wisely, nonetheless.