Sometimes some people notice that after the rain has passed, the water in the sea, river or in any body of water becomes warmer. This phenomenon, like many others, has its own explanation.
Explanation from a physical point of view
After a downpour or even a light rain, it seems to you that the water in the reservoir has warmed up. The thing is that when it rains, the ambient temperature drops quite sharply. As is known from the course of physics, in gaseous substances the distance between atoms is slightly larger than the radii of these atoms. Unlike gas, in water, the distance between atoms and their radii are approximately equal. From a physical point of view, we can conclude from this: it is much easier and faster to change the air temperature than to change the water temperature. From this it follows that when it gets colder outside during the rain, the water in the sea or in the river cools down noticeably more slowly. It will take 24 hours to lower the water temperature.
You can also note the fact that salty sea water in terms of density surpasses fresh river water. This means that the water in the sea cools down even more slowly than in rivers.
It turns out that from the point of view of physics, water does not get warmer, but keeps its temperature. So why, then, does a person feel that the water in the sea has become warmer?
Explanation in terms of human physiology
Since physics proves that the water temperature does not change, it means that the whole point is in the person himself, namely, in the difference in the temperature of the human body and water. When the sun is shining outside, the weather is warm and calm, the human body heats up quickly enough.
The difference in body and water temperature is palpable. Therefore, it seems to a person that the water is cold.
When the rain passes, it gets colder outside, as a rule, the wind blows, and the sun hides behind the clouds. The body temperature of a person becomes closer to the temperature of the water, and therefore, entering the sea, people feel that the water has become slightly warmer. But in fact, the water has kept its temperature, and the temperature of the human body has become lower.
A similar situation is with swimming in the ice hole, especially after the bath. When a person comes out steamed into frost, he feels cold. Water retains its liquid state of aggregation at zero or above zero temperature. That is why, jumping into the ice-hole, people do not feel the terrible cold, because it is even colder outside.
Now we can easily summarize all of the above. After rain, the water in the sea does not get warmer. It does not change its temperature at all, and a person only feels the difference in the temperatures of his body and the temperature of the water in the sea. The colder the body, the warmer the water appears in any body of water.