Maybe you know floods, earthquakes, sandstorms and so on. But have you heard of typhoons? Typhoons are some of the worst storms, usually around the Pacific Ocean and the South China Sea. Most happen in July, August and September. How does a typhoon happen? When lots of sea water gets hot in the summer sun, it evaporates  into the air. This makes the air hotter. When the air gets warm enough, it starts to move higher up into sky. Then cooler air around it rushes in. It fills the space that is left. After the air gets warmer, it starts to move quickly, making wind. The wind goes in circles and it keeps moving higher in the sky. The warmer the air gets, the quicker the wind moves. And when the wind moves faster than 30 metres a second, a typhoon begins. A typhoon has two parts, one is called the "eye". In the eye, the wind does not move so fast. The other part is the wall of clouds around the eye. Here are the strongest winds and hardest rains. Typhoons are very dangerous. In November this year, Typhoon Haiyan killed 5500 people in Philippines. More people are missing. What to do when a typhoon hits? Stay inside. Close all the windows and stay away from them. Try to bring all of your things inside. Strong winds could even blow away your bikes! Listen to the radio or TV for important information. If you're told to go to a safer place, do it right now. Typhoons often happen  _  .
in the hot season in the cold season only in China under the sea