Weather Safety: The Difference Between A Tornado And A Hurricane

Although tornadoes and hurricanes both cause tremendous damage through wind and rain, there are some very definite differences between them.

It's easy to find similarities between the weather phenomenon we call a hurricane and the one we call a tornado. Both cause most of their damage through high winds and rain, and the arrival of both can cause evacuations, emergency warnings and general chaos. But there are numerous differences between the two weather systems, from the elements that form them to the type of devastation they leave behind.

The confusion between a tornado and a hurricane may stem from a common nickname- cyclone. Technically speaking, a true cyclone is a hurricane which forms in the Pacific Ocean. Some suggest that a cyclone is a high-pressure storm system while a hurricane is a low-pressure storm system. When it refers to a tornado, it is almost always a regional nickname, not an official designation. Tornadoes may also be called twisters or funnel clouds.

A tornado is an isolated storm event which almost always forms ahead of a front. Certain storm clouds begin to strengthen into 'supercells', and the collision between the high pressure and low pressure systems causes the winds to circulate around each other. While the storms along the front and the supercells appear on radar, tornados

are rarely spotted until they've formed at least a measurable circulation of air. Tornadoes can form quickly, touch down for a few minutes and then spin back into the supercell. They may also remain on the ground, generating winds up to 250+ miles per hour, and cover a large swath of land.

Hurricanes, on the other hand, are systems within themselves. The entire system forms from a low pressure system generally located in the tropics. The heated ocean water serves as fuel for the cloud formations, which slowly begin to form bands of rain clouds around the center of the low pressure. Pushed further into the ocean by prevailing winds and the jet stream, a potential hurricane begins as a 'wave', then a 'depression', followed by 'storm' when the sustained winds are between 39 and 74 miles per hour. By this point, national meteorologists usually assigned a specified name to the system, following an alphabetical progression. The first named tropical storm or hurricane begins with A, the second with B and so on. Once the sustained winds reach 75 miles per hour, the storm is officially a hurricane. Unlike a tornado, the formation of a hurricane can be detected early and precisely measured throughout its life.

Tornados in general can generate much stronger winds than hurricanes, but do not last nearly as long. The damage from an average tornado is limited to the actual path a funnel cloud took during the limited time it touched the ground. The accompanying storm may cause additional damage through lightning strikes or heavy rain, but the tornado itself causes the most trouble. Hurricanes pack high winds and tremendous rains, but the long-term damage is often caused by the floods which proceed it. Hurricanes force the ocean water ahead of them to build into high waves known as 'storm surges'. Combined with the natural high tides, these surges can overwhelm coastal areas and cause widespread power outages and flooding. Tornadoes do not generate storm surges, but large hail may be a secondary problem victims face.

Tornadoes are measured by the Fujita scale- a system which assigns levels of destructive power based on post-storm assessments. This scale runs from an F-0 storm which causes little to no measurable damage all the way to an F-5 which can completely eliminate all structures in its path. Most tornadoes are in the F-1 to F-3 range, but these measurements are generally assessed AFTER the event. Estimating the power of a tornado while it is occurring can be very difficult.

Hurricanes are measured by category. Once the winds become higher than 75 miles per hour, the hurricane is considered to be a Category 1 storm. The highest category is 5, which generally occurs while the hurricane is over open water. Once a hurricane reaches a land mass, the energy of the heated ocean water is cut off and the 'engine' will begin to sputter. Depending on the size and stability of the hurricane, it can last for days or weeks. Tornadoes rarely last more than a few hours.

Tornadoes form over land, so they are not dependent on water for fuel. They exist only as long as the colliding fronts remain unstable enough for circulation to occur. Once the storm clouds lose their momentum, the possibility of a regeneration become minimal. Hurricanes, on the other hand, form over water and are dependent on the evaporating water vapor for fuel. They may weaken over land temporarily, but they will often restrengthen once they are back over water. A hurrican system can last as long as the low pressure center remains strong and a larger system doesn't shear it apart.

Perhaps the most important difference between hurricanes and tornadoes are the safety warnings. Tornadoes can form within minutes and a tornado warning may only be issued after the fact. Hurricanes have loosely defined courses which they will follow unless acted upon by a stronger force. This means that residents in the path of a major hurricane can be warned several days ahead of the storm's arrival. Specific details such as storm strength and general direction can be provided right up until the moment a hurricane makes landfall. Tornado signatures on radar can predict the general path of a tornadic storm, but specific details can be few and far between until the storm is already on the ground.

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