Weather Blog

Do hurricanes rain salt water? And why isn't our own rain salty?

Do hurricanes rain salt water? And why isn't our own rain salty?
When a hurricane rages in the Gulf of Mexico or Atlantic Ocean, you might think since it's churning along over such a large area of salt water, that its accompanying rain is full of salt? Same goes for our rain from storms born in the salty Pacific Ocean -- why doesn't it rain salt water here?

But it doesn't. In fact, all the rain -- no matter where in the world it is -- is freshwater (mostly. See below).

Why? It has to do with the evaporating process. When water evaporates from the ocean, only the pure H2O molecules are involved -- it's basically energy turning the water from liquid state to vapor state. The salt particles are left behind.

I'm not an oceanographer, but I would assume that means when you've got a really big storm, like a hurricane, taking in a lot of moisture from the warm Gulf/ocean waters, the salt content of the water in its wake is probably a miniscule higher, but negligible compared to the vast volume of the water.

Now that said, there are a few ways to get a salty rain, but it doesn't involve evaporation.

Communities along the coast deal with salt and rust from wind blowing in spray off the ocean. In that case, it is salt water because you are transporting water droplets directly from the water. Same with hurricanes and their storm surges and wind-whipped spray off the surf -- that is all salt water.

Also, there have been noted cases where a waterspout -- a tornado over water -- has sucked up sea water into the sky and carried it over land where it "rained" salt water. That is no different than taking a straw, sucking up some salt water, then spitting it out.

Other random notes:

* Rain water isn't 100% clean. To form, a raindrop needs some sort of particle to cling to -- usually this can be a speck of dust or dirt or soot or whatever. (That's how you can get acid rain, if the drops cling to sulfur particles or other pollutants). But it can also be a particle of salt, so you could technically get a raindrop that has a tiny amount of salt in it, but it's negligible and is still considered fresh water.

* Around the Northwest -- and especially during the mornings in the late spring through summer -- you can get a milky, whitish haze in the sky on otherwise clear days. That's when we have a weak to moderate flow from the west off the ocean blowing in salt particles from sea spray, which can give the sky a little tinge of white, and it's different than the smoggy brown tinge the city areas see during inversions.