Dear Tom,
I am wondering about the “brown ocean effect” with respect to the rain in the upper Midwest. It seems like it rains all the time once the ground gets wet. Does it occur there?
—Tom Ehret Darien


Dear Tom,
The “brown ocean effect” refers to a landmass saturated by heavy rain from an approaching tropical cyclone. Normally, landfalling tropical storms quickly lose strength, a result of the loss of latent heat from the ocean. If pre-landfall rain has been heavy, the saturated soils provide a moisture-rich environment, allowing the landfalling storm to maintain its strength or even intensify as if it were still over water. This phenomenon can also occur to a much-lesser degree in the Midwest when wet soils provide additional moisture to the atmosphere, resulting in more cloudiness, lower afternoon temperatures and enhanced rainfall.