Niwa says spring expected to be a normal old season - at last
Saturday, 18 August 2018
After record-setting seasons, spring is expected to be… well, pretty much like spring. But be warned: an El Nino summer approaches.
Niwa's latest report said despite a continued slow warming of ocean surface temperatures in the Pacific, July witnessed a slight weakening of the El Nino-like signals that emerged in June.
'Most notably in the subsurface ocean and in the atmosphere,' Niwa meteorologist Ben Noll says.
'However, intra-seasonal activity that recently developed in the far western Pacific might tip the system back to a more El Nino-like state in the next few weeks.'
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Niwa's climate outlook for spring forecasts near normal rainfall totals for the country with temperatures near average in the North Island, but above average in the South Island.
From August to October soil moisture levels and river flows are forecast to be near normal in the north and east of the North Island. However, in the east of the South Island, Niwa forecast below normal soil moisture levels and river flows.
'There will inevitably be wet and dry days, and hot and cold days, within a season. The exact range in temperature and rainfall within each of the three categories varies with location and season.'
However, it could be the calm before the storm as the probability for El Nino conditions increases as we approach summer in the Southern Hemisphere - Niwa says there is a 78 per cent chance for El Nino conditions from February to April 2019.
The strength and characteristics of this event - if it eventuates - remain uncertain at this point, but indications so far are that it is unlikely to be in the strong category.
WHAT DOES EL NINO MEAN?
In New Zealand, it's a game of two halves. With the east and west coasts in both islands separated by mountain ranges, each coast will have its own summer experience. The strong winds coming from the west will bring hot and dry weather to the east coast, and it will be wet, wet, wet on the West Coast.
It also means that the warmest months will be January and February. December is more likely to be on the cooler side.
In a nutshell, it does not guarantee a drought for the east coast, but it is more likely to occur than in a non-El Nino summer.
WEEKEND FORECAST
Most of the country is expected to see a bit of sunshine and a shower or two. Those showers could turn heavy for the west from Taranaki to Wellington, including Taihape and Wairarapa.
A complex trough of low pressure moving northeast over the North Island is replaced by a ridge of high pressure over the South Island. The ridge spreads over the rest of the country later on Saturday, and the trough weakens about Bay of Plenty on Saturday night.
Auckland, Hamilton and Tauranga are all forecast to reach 15 degrees Celsius. It's a chilly 10C for Wellington, and in Christchurch and Dunedin, a maximum of 11C is expected.
Snow on the Desert Road. Although SH1 is currently open, watch out for snow near the summit, as shown in the webcam image which can be found here https://t.co/E5dOOToqce. For all of MetService's road snow warnings head to https://t.co/aIkbAHKg1S ^TA pic.twitter.com/BITL09ao0O
— MetService (@MetService) August 17, 2018
On Sunday, the North Island is forecast to be fine with morning frosts and cloud developing in the north from evening. In the South Island, it'll be fine and frosty in the east with cloud developing in the west.
Looking ahead to Monday, rain could develop in the morning, with heavy falls possible for Taranaki, Bay of Plenty and the central North Island. Cloud is increasing in the east with brief rain.
In the South Island, rain in the west, possibly heavy, and cloudy with a few spots of rain in the east.