In the beginning, the ocean storm is called a "tropical disturbance", which is like a bunch of thunderstorms with very little wind circulation. When wind speeds up to 20 to 34 miles per hour, the ocean storm becomes a tropical depression. A tropical depression can quickly become a tropical storm if the wind speeds reach 35 to 64 miles per hour. Once the whirling mass of air grows and continues to spin around a center of low pressure, wind speeds increase. When wind speeds reach 74 miles per hour or greater, the storm is considered a hurricane and given an official name.
Hurricanes are large storms with rotating winds. They form over the warm waters of the ocean when there are large pressure and temperature differences between the warm water and the clouds. The clouds pull the moisture and the air near the surface of the water up, toward the clouds, which creates a column of fast-moving air.
Sometimes the air in one place is warmer than the air in another place near it. Warm air is thinner and lighter than cool air. When heavier cool air touches warm air, it presses against it and pushes. Some of the warm air moves sideways, and some of it moves up. As the warm air keeps moving to the side and up out of the way, the cool air flows in to take its place. This movement of the air is the wind. Most of the air all over the surface of the earth is moving, a little or a lot, most of the time.
Fun Facts About Hurricanes *Hurricanes may have a diameter of 400 to 500 miles(640-800 kilometers) *The "eye" or center of a hurricane can be up to 20 miles(32 kilometers) *The weather in the "eye" is surprisingly calm with low winds and clear skies *Hurricanes hit land with tremendous force, bringing huge waves and heavy rain *Many hurricanes cause severe flooding *About 90 percent of the deaths that occur during hurricanes result from drowning in floods *The world's worst hurricane (for loss of life) took place in 1970 in Bangladash. That hurricane created a flood that killed more than one million people
Most twisters or cyclones travel from southwest to northeast and can move in the opposite direction for short periods of time. A tornado can even backtrack if it is hit by winds from the eye of the thunderstorm
Fun Facts Damage paths of tornadoes can be in excess of one mile wide and 50 miles long. Funnel clouds usually last less than 10 minutes before dissipating, and many only last several seconds. On rare occasion, cyclones last over an hour, and many were recorded this way in the early 1900s. A tornado may appear nearly transparent until dust and debris are picked up or a cloud forms within the funnel. Tornadoes can accompany tropical storms and hurricanes once on land. Tornadoes are most likely to occur between 3 and 9 pm, but can occur at any time.
Snow forms when the atmospheric temperature is at or below freezing(0 degrees Celsius or 32 degrees Fahrenheit) and there is a minimum amount of moisture in the air. If the ground temperature is at of below freezing, the snow will reach the ground.
Sleet is formed when raindrops pass through very cold layers in the atmosphere which causes them to freeze. It can also be formed when snow passes through warmer layers and partially melts then quickly passes through another cold layer.
On a hot summer day the surface of the Earth is heated by the sun. The Earth's surface heats the air just above the surface through the process of conduction. The action of warm air rising and cold air sinking (convection) plays a key role in the formation of severe thunderstorms. If the warm surface air is forced to rise, it will continue to rise, because it is less dense than the surrounding air. In addition, it will transfer heat from the land surface to upper levels of the atmosphere through the process of convection. Two of the most important ingredients for thunderstorm formation are instability (unstable air) and moisture.
Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated- that is, become heavy enough to fall under gravity
Fun Facts The most rainfall ever recorded in one year is 25.4 meters(1000 inches) in Cherrapunji, India. Rain occurs on other planets in our solar system but it is different than the rain we experience here on Earth. For example, rain on Venus is made of sulfuric acid and due to the intense heat it evaporates before it even reaches the surface!