Warm in Wellington, windy up north
Wellingtonians have been basking in an usually warm and calm start to July.
While Northland prepares for storms and high wind gusts later today and into the evening, NIWA forecaster Chris
Brandolino says the temperature in the capital is well above average for this time of year.
“The daily maximum temperature for the first week of this month is 12.8°C, or 1.4°C above average – and these mild
winter daytime temperatures may continue through until the end of this weekend,” he said.
Mr Brandolino says the culprit behind the wind and rain for the top half of the country, is a combination of a storm
over then northern teaming up with a high pressure system southeast of NZ. The two are producing what is called a steep
pressure gradient, or change in air pressure over distance. The low centre over the eastern Tasman is forecast to reach
around 990 hPa this evening. Meanwhile the surface pressure associated with the anticyclone southeast of the country is
forecast to have a central pressure of around 1033 hPa.
“Air flows from high pressure to low pressure, like water flowing from the top of a hill to the bottom of a valley. The
sharper the drop in elevation, the more quickly the water flows – it’s the same idea with a rapid change in air pressure
over distance.”
The difference in air pressure, or pressure gradient, between these two system becomes steep over the North Island, as
does the wind, is a playing a large role in the intense east to northeast wind.
This east to northeast wind is bringing with it subtropical moisture and providing fuel for the heavy rain north of
Auckland.
Winds will ease, but not until later tomorrow, as the low over the Tasman weakens.