By the time the first drops of water begin to fall, the asphalt tends to push dirt onto the road surface, including dirt and oil residue. The combination is extremely dangerous and can lead to the vehicle skidding at the least expected time.
On the other hand, once the rain has already fallen steadily and in abundance, there is a good chance that rafts of water will form in certain areas of the road. These are very dangerous situations, especially when driving at high speed.
This phenomenon, known as aquaplaning, involves a substantial or total loss of traction and direction of the vehicle. In addition, due to its characteristics it is difficult to perceive it early enough.