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There is a variety of highs and lows moving through NZ in the weeks ahead bringing changeable wind directions and temperature swings. Rainfall looks broken up with the chance for some heavy falls but many regions may still miss it – due to the messy nature of these rain bands.
At this stage big belts of high pressure look to remain crossing Australia and into NZ but they may be further north than last month, encouraging more westerlies into the nation. We take a look at the likely trends going through June as our “neutral” weather pattern encourages a messier set up.
Despite rain falling in May, a number of regions like Nelson, Marlborough and Canterbury are drier than average from a soil moisture point of view, along with southern coastal Taranaki, Whanganui, Manawatu, Horowhenua and Wairarapa in the North Island. This part of central NZ has missed out on some of the bigger rain events so far this autumn.
The first half of June may not bring much relief to all of these regions – but the neutral pattern brings more chaos factor into all of Australasia and that can be a better set up for those needing a break from the drier than usual weather we’ve had so far this year.
The model of all models shows all reliable global models (excludes NIWA from NZ who are commercial with no open data) displaying we’re in a “neutral” period now and may linger for months in this place. Some modelling suggests La Nina is likely later in spring but this is still long from being confirmed still. Graphic credit: BoM.Global modelling shows we’re neutral right now.Global modelling by late winter still suggests we’re in a “neutral” phase but that the signs of La Nina are developing further.Into mid-spring and some modelling, like NOAA from the USA and the British UKMO models pick La Nina, but Australia, France and European modelling less certain, although worth noting no global models lean towards El Nino by this point.Week 1 of June kicks off with a mild and windy westerly flow over NZ due to high pressure north of the country. This northern high pressure zone actually spent the second half of May parked over Tasmania… so for it be moving on is a good thing for those who need a change from May’s pattern. As we go through Week 1 low pressure will likely form off the coast of NSW and remain in the Tasman Sea area across next week. There may be a colder southerly flow for a time too (variety in wind flows means changeable temperatures).By Week 2 that low pressure zone near Australia looks to drift into NZ…but at the same time a slither of high pressure makes it over the lower South Island. This creates an easterly flow for some in the middle or north of the nation. The low itself is messy and hard to lock in this far out, especially with regards to if it will produce good rain, or fall apart. It’s worth monitoring later in June’s first week and going into June’s second week.By Week 3 (Mid June) low pressure may be affecting NZ – but at the same time another power area of high pressure returns to Australia. June’s weather systems do look to move through faster than May’s ones, but these big highs and lows may still be slow moving compared to usual conditions in June. Modelling becomes far less reliable after this point so we don’t include beyond Week 3.Departure from Normal Rainfall shows Australia has better chances for rain with some in the dark blue getting 800% normal rainfall. But those in red and pink only getting 5 to 75% of normal rainfall (for this time of year).15 Day Expected rainfall. Areas in white have least amount of rain, areas in black have highest totals.A closer view of NZ over the next 15 days shows eastern parts of the South Island will be driest (although rivers and streams coming from the mountains should get some spillover rain from the West Coast). The rain forecast for the upper North Island is less certain and is due to the large low in the Tasman Sea for first week or two of June – and precise tracking into NZ was still unclear at the time we put this ClimateWatch outlook together. It’s possible it will be further north of NZ.Sea Surface Temperature Anomaly map – in other words, how much warmer or cooler is the Pacific Ocean for this time of year. Around NZ it’s either normal or just slightly above normal. To our north in the tropics it’s becoming warmer (Classic sign of La Nina developing). Map courtesy: BoM.
WeatherWatch.co.nz – NZ’s largest private forecaster.
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