Why is the wind gusty?

With Storm Ciara in full swing, I was wondering about a question that I've never answered: why doesn't the wind blow at a steady speed? Why does it have gusts? The best short answer I've found is this: https://wxguys.ssec.wisc.edu/2012/01/09/what-causes-wind-gusts/ I suppose that it is no surprise that flowing round objects changes speed. There is variation when air flows over an aerofoil - the air goes faster over the top than the bottom to ensure flow rate remains constant. The same is true for flow round a swinging cricket ball. But I'm interested that they say it isn't gusty until the average speed reaches 18mph.