Explanation: Why it's been so windy over NZ


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After what has been a windy past two weeks for some areas the winds are today finally light for most as a deep low in the Southern Ocean moves away to the east, while a large high in the Tasman drifts closer to us.

The air pressure gradient was a staggering 60 to 70 hectopascals (hPa) between the two systems.  Air pressure, which is shown as isobars on weather maps, is similar to the lines on topographical maps.  The closer together the steeper the gradient (and the windier it is).  The more spaced out those lines are the lighter the winds are due to a far more gentle gradient.

Most highs around New Zealand are in the 1005 to 1020hPa range.  Most lows are usually around 980 to 1000hPa. 

At one stage the high in the Tasman was close to 1030hPa and the low to the south east was 960hPa.

On a topographical map that would look like a steep mountain range!

It's this "mountain range" in the air that creates the wind.  The steeper the slope the stronger the wind. 

The 'squash zone' is the area where the isobars are tightly packed together, where the air pressure falls/rises the most over a certain distance.

For the past few days that squash zone has been right over New Zealand but actually the worst of the winds remained just off the south east coast of the South Island - which is why coastal Otago and coastal Southland received the worst of the winds on Friday night.

As the high moves in and the low rolls away the winds will ease too... but unfortunately for many it does return on Monday, so make the most of a calmer Sunday.

WeatherWatch.co.nz expects windy weather, off and on, to continue well into December and possibly right up until Christmas but the worst of the winds should start to ease in the coming weeks.

- Homepage image / File, Taylor Shea

- WeatherWatch.co.nz


Comments

Nice description!

I learnt about all this in intermediate school and most of it stuck, but I really like your description - it's a nice comparison!

Out of curiosity, and I know you may well have talked about this before, but what kind of conditions are we expecting for the summer? Will it be hot, dry and windy or wet and humid?

Thanks!

Today was a contrast to

Today was a contrast to several earlier ones here - fine with a bit of haze and odd patches of very thin cloud, light southerly breezes. Very pleasant.