The cool water doesn't. Now, imagine you fill your bathtub with hot water. Think about how warm and steamy the air in the bathroom gets. Now, imagine millions and millions of bathtubs-ful of hot water. All of that moist, hot air has to go somewhere.
Scientists know that hot air rises and carries the moisture with it.
Once the moisture gets into the air and starts to cool, rainclouds start to form. The moisture in the air should collect on the mirror, and, as it cools, form tiny droplets. Imagine the bathroom mirror after you fill the bathtub with hot water. Now imagine the air over the hot water of the tropical Pacific Ocean. Huge rainclouds start to form and flooding results in South American countries along the coast.