The Southern Hemisphere polar vortex took a unique journey this winter. 
A mid-July, minor Sudden Stratospheric Warming event saw the vortex become elongated, weaker, wobbly. This stratospheric anomaly affected tropospheric weather patterns, but now appears to be easing. In late July and early August, a rapid stratosphere-troposphere coupling contributed to the development of a major high pressure cell and heatwave over Antarctica, while a very deep low formed over the Southern Ocean, and a heat dome affected Australia. It was associated with relatively cool conditons in Chile and Argentina.
New Zealand experienced, and continues to experience, rounds of strong, westerly winds and active weather because of this. However, mid-to-late September may take on a different flavour, as a La Niña-like weather pattern takes shape and grabs hold of Mother Nature’s “steering wheel”. This may result in the formation of a blocking high pressure system to the south-east of the country and a slowing of the general weather patterns.
Read also: The rare event driving the Southern Hemisphere’s weather | NIWA
An unusual disturbance high above Antarctica is causing polar air to encroach on different parts of the Southern Hemisphere, including New Zealand. Every winter, a ring of stormy, freezing weather – known as the polar vortex – encircles Antarctica. Typically, it keeps harsh, wintry conditions locked up near the south pole. NIWA meteorologists discussed the polar vortex in their just-issued Seasonal Climate Outlook for August-October.
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