Barrel Rain

"What?"
-A Sailor Who Has Heard Too Much Barrel Rain

Cannonfire Raindrops

This strange weather phenomenon occasionally occurs in the northern sections of The Wild Sea, best known as Barrel Rain, or sometimes Thunderdroplets. A strange and mildly magical set of weather conditions lead to the occurrence of barrel rain, which is when a number of rain droplets within a rainstorm are filled with compressed air. When the droplets contact anything, the air within them rapidly expands, causing a distinct loud popping sound which vaguely resembles a gunshot. With so many droplets popping at once, being in barrel rain sounds like a constant firefight.

Harmless To All But The Ears

Barrel rain itself isn't actually too harmful to people - though being hit with droplets hurts about as much as being hit with a snapping elastic band. Even a thin layer of cloth significantly reduces this pain though, so barrel rain barely has any capability to physically hurt you in the short term.
The main issue comes with prolonged exposure. While most people can tolerate the noise of a firefight for a few minutes, it quickly becomes an issue when your ears are exposed to the sounds of barrel rain for an extended period of time. Longtime sailors of the northern Wild Sea have been known to go deaf young. On the flipside, barrel rain can be good because it is able to startle rodents to death - so it's an easy way to deal with those kinds of problems for ships that have them.
Going below decks can help with the impacts of barrel rain, but ultimately the sounds can still be clearly heard. It's customary, then, to travel that portion of the seas with ample supplies of wax for people to put in their ears to drown out the sounds of the rain (and any ship with cannons usually has wax like that anyways).

Backdrop to Hidden Violence

It is said that for every 100 bursts of barrel rain, one is actually a real gun. When barrel rain comes, it's the perfect time for disguised violence. When somebody hears a gunshot during barrel rain, they aren't likely to think much of it. Most mutanies that happen in that region of the seas take place during barrel rain. The same is true for murders.
Because of this, some people take barrel rain as a sign of danger, and make a point to lock their doors at home or bring guns with them when outside to ensure their own safety.