Why is there a calm before a storm?



So I live on the South West Coast of Ireland and tomorrow we are expecting to be hit by the tail end of Hurricane Lorenzo. If you stand outside tonight, there isn’t even a puff of wind, just deathly calm. It’s eerie out there. Similar to a tsunami, is it a bit like all the wind has been sucked out beforehand?

In: Physics

As warm, moist air is pulled into a storm system, it leaves a low-pressure vacuum in its wake. … That descending air becomes warmer and drier which is relatively stable, and once it blankets a region, it stabilizes that air in turn. This causes the calm before a storm.

Wind is driven through pressure gradients. The stronger or more quickly the pressure changes over a short distance, the stronger the wind blows (from high to low). A storm like lorenzo has an amazing pull towards its low center. Its pulling air in, forcing it upward and then expanding it outward at the cloud tops.

Now, this inward pull of mass (air and moisture) and momentum causes the pressure gradient to become stronger the closer to the low pressure center. There needs a lot of mass going into it to maintain this gradient.

The abundance of mass entering, and packing the pressure gradient, needs to be balanced by a place elsewhere that has a pressure gradient that isnt as strong. So, what you are experiencing is the area where the mass is being initially evacuated from. Resulting in a pressure gradient that does not rapidly change over a short area, because it’s being spread out and pulled into the low center.

Tl:dr -> its mass continuity, in Lorenzo there is a strong pressure gradient force driven by an influx of mass towards its center. Its balanced by an area of calm further away from from it, where the pressure gradient doesn’t change as rapidly.

Thanks everyone for replying, makes so much sense now!