The Southern Ocean is most famous for it’s often ferocious weather thanks to bitterly cold air blasting north from Antarctica. However this week an intense high will drift in from the south of New Zealand to bring a mostly sunny, settled, 7 days for much of New Zealand.
“As far as anticyclones go this one is right up there in the ‘strong’ category. The air pressure will be over 1040hPa which is quite rare” says WeatherWatch.co.nz head weather analyst Philip Duncan.
“If you think of this high as a tyre filled with more air than usual…it bulges out over a larger area and its strength repels anything from pushing in to it”.
Mr Duncan says while it heads north west towards the North Island gusty sou’easterlies will move in ahead of it. “The ‘squash zone’ – the area between high air pressure and low air pressure where the isobars all bunch up – will spread over the North Island during Tuesday and Wednesday which means sou’easters could be a little breezy at times”.
Cloudy periods and a weak front may also bring in a few showers on Wednesday for northern New Zealand.
Eastern and northern areas of the North Island may see more cloud and lower daytime highs but possibly slightly warmer nights thanks to the winds.
In the South Island it’s a different story. “Frosts are definitely possible through inland parts of the South Island. Remember this high has moved cold, dry, air from the Southern Ocean. With no wind and low humidity the air temperature will fall significantly at night”.
Mr Duncan says because the pressure is so much higher in an anticyclone cloud is pushed to low levels, often to ground level to create what we call fog. “Overnight and morning fog and low cloud are possible throughout the country starting in the South Island Tuesday night and moving into the North Island once those sou’easters have eased back, perhaps around Thursday”.
By the weekend the high will be centred over the North Island while nor’westers will build behind it over the South Island. Sea breezes and light winds are expected for many parts of the North Island this weekend.
on 31/03/2009 8:34am
You must be careful when associating intense anticycones with fine weather. Sometimes cloud can be trapped underneath which results in what they call “Anticyclonic Gloom”. This can produce dull days and drizzly rain.
on 30/03/2009 11:57pm
Thanks Philip – I really enjoy your site and find it most informative. I can understand weather patterns so much better now, after many years of listening to meaningless technical data!