Everyone knows the destructive force of a hurricane. They have the power to pull houses off of their foundation, sweep cars away and destroy almost anything in their path. With all the destruction in mind, few people stop to think about what a hurricane actually is and how they are formed. The simple answer to the question is easy: Wind. However, there is much more science to a hurricane than that.
For a hurricane to form, the right conditions are needed. First and foremost, hurricanes form over water, so water itself is needed. Not just any water will do, though. Water temperatures must be above 80 degrees Fahrenheit (27 degrees Celsius) for a hurricane to even be possible. It is for this reason that hurricanes primarily form in tropical regions. In fact, hurricanes start out as clusters of thunder and rain storms in tropical regions – earning them the name tropical disturbances. Tropical disturbances contain little to no rotation and usually dissipate before much becomes of them. Some of the tropical disturbances release their latency heat, which lowers the air pressure and moves them on to the next step.
This is where the science really comes into it. When converging winds hit the moist air of the storms, they drive the warm, low pressure air upward. As a result, cool, high pressure air swoops in underneath. This is known as the Pressure Gradient Force. The process causes wind speeds to increase. These wind speeds themselves would not mean much without the following step – the Coriolis force (sometimes referred to as the Coriolis Effect). The Coriolis Force is caused by the Earth's rotation. It is a rather easy principle to follow. Simply put, as air is flowing, the Earth is rotating under the flowing air. This causes the air flow to change to a curving direction. In the Northern Hemisphere, the air curves to the right, while in the Southern Hemisphere, it curves to the left. So what does this have to do with hurricanes and the increasing wind speed? Well, the Coriolis Force causes these strong winds to curve. At this point the storm starts to rotate.
When the rotation begins, it pulls in more moisture. The moisture starts to condense and creates additional cloud activity. Pressure high in the atmosphere continues to remove the warm air and the storm increases in size. At this point, the storm is considered a Tropical Depression. When wind speeds top 39 mph, it becomes a Tropical Storm. At over 74 mph, the storm is officially a hurricane. It can grow in size as long as it continues to get warm, moist air and meets optimal wind conditions. The whole process can take anywhere from a couple of hours to a number of days.
When all of these conditionals are met, hurricanes can develop. All in all, about 40-50 hurricanes form each year. Of that, only a small number actually make it to land. When they do, be prepared or be somewhere else!