The Equinox happens twice a year, and is the point at which day and night are of equal length.
The Spring Equinox brings the wildest weather - and this is because in spring, Antarctica is at it's coldest for the year, while the Equator is very warm - the biggest differential in temperatures occurs and causes strong winds. In Autumn, Antarctica is at it's warmest, and so the temperature difference between it and the Equator is much less, though we can still expect unsettled weather close to the Autumn Equinox.
Weather can be unpredictable, but when regular patterns occurs, it pays to be aware of and prepared for them. The high-winds of September are another reason to keep seedlings protected, and are why I haven't already got all my seeds planted. I'm hoping for a few calmer days soon. This is also why I prefer to have our sheep lamb in July - our lambs are a good size before September, and much more able to withstand cold, wet, windy, miserable weather.