HowItWorks.net

What Is A Hurricane?

In its simplest terms a hurricane is a storm system of very strong winds accompanied by clouds and heavy rain - which circles around a calm center. This calmness in the center of a hurricane, often referred to as the “eye of the storm” can literally lull people into a false sense of security; and thinking that the worst of the hurricane has passed they either open their doors and windows or worse venture outdoors, only to be caught out by the hurricanes second phase. Although anyone in a hurricane will experience very heavy rainfall, the key feature they will experience is, beyond doubt, the incredible strength of the wind.

So How Does a Hurricane Work?

Hurricanes begin over warm tropical seas with the movement of a mass of air. The movement of air, wind, is caused by changes in atmospheric pressure as the air warms and cools due to the heating effects of the sun. Warm air is under higher pressure than cold air and so moves towards the ‘space’ occupied by the colder, lower pressure, air. The speed with which the air moves, from a high pressure space into a low pressure one, depends on the differences in pressure between the two spaces. A small difference in air pressure results in a gentle wind. A large difference in air pressure will result in a high wind.

How A Hurricane Is Born

The risk of a hurricane forming arises on occasions when the air movement starts to circle; specifically when the air pressure on the inside of the circle is extremely low compared to that on the outside. As the higher pressure air spirals inwards, around the lower air pressure over sea water, it whips up the sea creating huge waves and a lot of water spray, adding moisture to the already high level of water vapor in the air. Since all this is happening in tropical waters, we’ve got warm and wet air spiraling at speed and - remembering your High School science - the warm wet air rises. But as it rises, so then it begins to cool. Subsequently, the water vapor condenses to form first clouds and then rain.

Fanned by the Heat of the Tropics

Due to the tropical heat the rainfall evaporates again, re-heating the rising air, which in turn causes it to rise faster and increase its speed even more. As the air continues to heat up it carries on expanding, rising ever further upwards to heights of 10 to 15 kilometers. From that sort of height when the air eventually cools it falls to the outside of the storm, outward and over the top, away from the eye of the storm. However, in doing so it reduces the mass of air over the ‘eye of the storm’ - causing the wind speed to increase further and making the already highly saturated humidity of the air even wetter. When this cycle of events continues over warm seas the whole weather system, hurricane, simply gets stronger and stronger. The stronger the wind blows, the lower the air pressure in the storm's center becomes and so develops into a powerful and violent force of nature - a hurricane.

Hurricanes in the USA

Developing over warm tropical seas, many of the hurricanes affecting the USA occur around and enter land from the Gulf of Mexico. Hurricanes can sometimes blow themselves out after first hitting the Caribbean islands before arriving at the US mainland. However, individually hurricanes have very different levels of force, strength and sustainability, all of which are also difficult to predict. Some hurricanes are so strong that even after hitting many of the islands in the West Indies before reaching land in the USA, their strength will not be reduced; nor will it prevent them causing damage rated at natural disaster levels. The USA has developed hurricane warning systems and people living in areas susceptible to hurricanes are always told to listen in carefully to weather forecasts between June and November. For most hurricanes hitting the USA, having hurricane shutters for your windows and doors will provide reasonably adequate protection. Incidentally, hurricane shutters are also known as plantation window shutters, due to the historical associations with the cotton and tobacco plantation farmers in these Southern regions of the USA that are more commonly affected by tropical storms.

Some Information on Wind Speeds

In 1805, a system for categorizing and measuring wind speeds was drawn up by and named after Beaufort, an admiral of the British Royal Navy. The modern version of this Beaufort scale was developed in 1946 and has 12 categories measured in kilometers per hour. On the Beaufort scale, a ‘gentle breeze’, sufficient to move leaves and twigs on a tree would be classed as 3 on the scale - 12 to 19 km/h. At 7 on the scale is a ‘high wind’ - 50 to 61 km/h, sufficient to make whole trees sway and be awkward to walk against. The highest Beaufort scale number is 12 - Hurricane force, for winds greater than 117 km/h; sufficient to hurl debris and cause damage to buildings. At this point hurricanes enter into a classification of their own, known as the Saffir-Simpson Scale, which was developed in the 1970s:

Category Name Wind Speed (km/h) Description
Tropical storm <118 Very weak
Category 1 119-153 Weak
Category 2 154-177 Moderate
Category 3 178-209 Strong
Category 4 210-249 Very strong
Category 5 >249 Devastating

Alternative HTML for the above table layout - you will need to remove one!

Category Name    Wind Speed (km/h)     Description
Tropical storm              <118                       Very weak
Category 1                  119-153                   Weak
Category 2                  154-177                   Moderate
Category 3                  178-209                   Strong
Category 4                  210-249                   Very strong
Category 5                  >249                        Devastating

About The Author
Julian Pollock is an enthusiastic environmentalist and the editor of Polycore Shutters, a site that provides essential information about the various sorts of traditional wooden, modern synthetic and the latest environmentally friendly shutters on the market.