Typhoons form in all tropical oceans except the South Atlantic Ocean. They have very low atmospheric pressures, warm centres and strongly developed tropical cyclones. Typhoons have different names in different locations. In the northwest Pacific and the South China Sea, they are called typhoons. In the North Atlantic and the Caribbean, they are called hurricanes, while in the Indian Ocean and the Bay of Bengal, they are called tropical storms. Since 1989, China has used the international names for tropical storms if a tropical cyclone reaches maximum winds speeds of grades 8–9. When the wind speed of the centre reaches grades 10–11, it is called a severe tropical storm. When the wind speed reaches grade 12, it is called a typhoon. Typhoons occur with strong convection, very strong and destructive winds and torrential rains. They are considered a natural hazard and pose a threat to human life and property.