I have fielded several questions the past few days about why the rain from a hurricane doesn’t fall as salt water since the storms gain all their strength over the ocean waters?
One viewer asked “If Irma sucked up water from the ocean which could fall on Indiana as rain, what happens to the salt?” These are very good and legitimate questions after we saw the flooding from Hurricane Harvey and the storm surge from Hurricane Irma.
Let’s start with the topic of the rain being salt water and being “sucked” up from the storm. Tornadoes would have the capability to pick up say some salt water and deposit over land. However, the process of hurricane development is very different.
Irma, or any other tropical systems don’t “suck” water up from the ocean. The moisture in a tropical system is generated purely through evaporation. During the evaporation process salt water would turn into water vapor, which is a gas. The salt would thus be left behind in the ocean.
The next process is condensation. As the water vapor is lifted it cools. As it cools it condenses and forms a cloud which then could produce rain. However, since the salt was left behind in the evaporation process any rain that falls would be salt-free water. This was the case in Houston where the flooding was a result of heavy and continuous rain.
With Irma we also had some flooding which was salt water. This was much different. This was a combo of rain, persistent onshore winds and also the storm surge. The storms surge and winds literally pushed the ocean water inland. This type of flooding usually recedes fairly quickly after the storm passes.