Hurricanes are among the most violent storms on Earth. Depending on their geographic location, they are also known as typhoons or cyclones, but they all form the same way. The scientific term for hurricane, typhoon and cyclone is ‘tropical cyclone’. The tropical cyclones that form over the Atlantic Ocean and the eastern Pacific Ocean are called hurricanes.
A tropical cyclone can be compared to a giant steam engine that use warm, moist air as fuel. That is why hurricanes do not form near the North or South Pole, the form only over warm ocean water that is at least 80 degrees Fahrenheit or 27 degrees Celsius. This warm water is located at or near the equator. Storms that form North of the equator always spin counterclockwise, winds in storms that form South of the equator spin clockwise.
When conditions are right for a hurricane to form, the warm, moist air over the ocean rise upward. This warm air move up and away from the surface, there is less air left near the surface and this causes an area of lower air pressure. When warm air rise and leave the low pressure area, surrounding air – with higher air pressure – make its way to the low pressure area. The warm, rising wet air begin to cool off and form clouds.
This system of clouds and rising air continue to spin and grow as the warm, moist air continue to rise. The warm, moist rising air from the ocean continue to feed the clouds and strengthen the resulting winds.
When the winds in the storm reach 39 mph, it is officially called a tropical storm. The warm air keep rising, making clouds that grow and these clouds sometimes grow to several miles across and as tall as 20,000 feet high. These tall clouds are called cumulonimbus clouds. A tropical cyclone is made up of several of these clouds.
As the enormous system continue to grow and rotate faster and faster, a clear, storm-free area forms in the center of the storm – called the ‘eye of the storm’. The eye is filled with very low air pressure, the high pressure air from above flows down into the eye. When wind speeds in the storm get to 74 mph, it is officially a ‘tropical cyclone, or hurricane.
The area around the calm eye is called the eye wall. This is where the most violent winds occur, along with groups of severe thunderstorms that circulate outward – called rain bands.
Hurricanes usually start as clusters of clouds and thunderstorms called tropical disturbances. Most of these disturbances dissipate, but several continue to swell into a tropical storm and these storms grow into a hurricane. It can take anywhere from a few hours to several days for a tropical disturbance to develop into an official hurricane.
* Tropical Depression: wind speeds of less than 38 mph
* Tropical Storm: wind speeds of 39 to 73 mph
* Hurricane/Tropical Cyclone: wind speeds greater than 74 mph
Category One Hurricane (Sustained winds 74-95 mph
Category Two Hurricane -Sustained winds 96-110 mph
Category Three Hurricane – Sustained winds 111-130 mph
Category Four Hurricane – Sustained winds 131-155 mph
Category Five Hurricane – Sustained winds greater than 155 mph
Each year, between June 1 and November 30, 80 and 100 tropical storms develop throughout the world, but most of them do not reach hurricane status. Even though hurricanes weaken when they make landfall, they cause wind damage and flash floods from the huge amount of rain they bring. Stay safe during hurricane season by listening to weather reports and warnings..