Over tropical oceans, the temperature of sea surface rises when heated by direct solar radiation, sea water evaporates off and generates water vapor, dispersing in the air. Therefore, both air temperature and humidity over tropical oceans are high. Such air expands due to high temperature, and becomes less dense and lighter. Also because of light winds around the equator, warm air rises and is replaced by the surrounding cold air which flows in and rises again. The air circulation continues and convection occurs. Eventually, the entire column of air consists of warmer, lighter and less dense air, which is called “tropical depression”. Air flows from areas of high pressure to areas of low pressure, as water flows from high level to low level. The surrounding air flowing from high-pressure areas to low-pressure areas forms “winds”. In summer, as solar radiation zone moves from the equator to the North Pole, the southeast trade winds in the Southern Hemisphere cross the equator and become the southwest monsoons entering the Northern Hemisphere. When the southwest monsoons meet the northeast trade winds in the Northern Hemisphere, air rises and forms strong convection. Since the southwest monsoons and the northeast trade winds have different directions, wind swirls and cyclones are often created when they encounter. The convergence is formed when the southwest monsoons meet the northeast trade winds. Under the combined effects with air convection, the formed cyclones of low pressure deepens, in other words, the air rapidly flows from the surroundings towards the center, the higher the flow speed, the higher the wind speed. When the wind speed near ground surface is at or above 62 km/h (i.e. 17.2 m/s), we call it a “typhoon”.