A ridge of high pressure is in place over Aotearoa, leading to mainly fine conditions. Strong northwesterlies ahead of a
front affect eastern parts of southern and central New Zealand early this week and MetService has issued warnings and
watches. The front then brings rain to the west of the South Island on Monday and Tuesday, and a few showers in the
east. The North Island is in for a brief spell of showers on Wednesday as the front goes through. Behind this front is a
cooler airmass, which brings a drop in temperature with the front. A new ridge establishes on Friday but is displaced by
another front during the weekend.
This changeable pattern is typical of the season. MetService meteorologist Andrew James explains “Spring is the windiest
season. Winds are driven by temperature difference over a large scale. At this time of year, the northern part of the
southern hemisphere warms up much faster the Antarctic, leading to the largest temperature differences and hence the
strongest winds. These strong westerlies move fronts over New Zealand at a rapid pace, so spring is typically
changeable”
The front brings rain to the west of the South Island from late today into tomorrow, and Severe Weather Watches have
been issued for heavy rain about the ranges. The Southern Alps provide sheltering for the east coast, so Cantabrians
should expect just a few showers tomorrow. The front weakens rapidly as it moves north, so the North Island is only in
for an hour or two of wet weather – starting for Wellington after dark on Tuesday and affecting Auckland on Wednesday
afternoon.
The front also drops temperatures. “A front is the boundary between two airmasses” says James, “warm air currently over
the country has allowed low cloud and fog to plague the mornings from about Whanganui northwards. Cooler air moves in
with this front and a ridge develops - the perfect setup for frosty mornings. Growers in both islands will have to be
alert from Friday morning.”
“The chilly start might be bit of a shock for Kiwis who had the shorts out after the warm weekend – especially for those
in the east, where the strong northwesterlies have driven up the temperatures. Blenheim is expected to reach 26 today
and then drop to 1C Friday morning, it is a similar story right up the east of both islands”