The cause of typhoon is uncertain, but it is known that it developed from the disturbance of tropical atmosphere. In the tropical ocean, the sea surface is exposed to direct sunlight, which makes the temperature of seawater rise, and the seawater is easy to evaporate into water vapor and spread in the air. Therefore, the air in the tropical ocean has high temperature and high humidity, and this air expands due to high temperature, resulting in the decrease of density and weight. The wind near the equator is weak, easy to rise, and convection occurs. At the same time, the surrounding cold air flows in to replenish and then rises again. This cycle will eventually make the temperature of the whole air column higher and the mass lower. Air flows from high pressure to low pressure, just as water flows from high pressure to low pressure, air with higher ambient pressure will flow to low pressure, thus forming "wind". In summer, due to the direct sunlight moving from the equator to the north, the southeast trade winds in the southern hemisphere cross the equator and become southwest monsoon to invade the northern hemisphere. When they meet the northeast trade wind in the northern hemisphere, the air is forced to rise, thus increasing the convection. Due to the different directions of southwest monsoon and northeast trade wind, when they meet, they often cause fluctuations and vortices. The convergence caused by the southwest monsoon and the northeast trade wind and the continuation of the original convection make the vortex with low pressure continue to deepen, that is, the air around it accelerates to flow to the center of the vortex, and the faster the flow, the greater the wind speed; When the maximum wind speed near the ground reaches or exceeds17.2m per second, we call it a typhoon. (? Source: Weather Network)