Formation of tropical storms

Matthew Mortimer

IntroductionThere are many different names tropical storms such as cyclone and typhoon. However, the storm is named by the location of its formation. Hurricanes start in the Atlantic, off the west coast of Africa. An average of around a dozen hurricanes form in the Atlantic each year. The hurricanes then travel westwards towards the Caribbean, the east coast of Central America and southern USA. Hurricanes can last as long as a month and although they travel slowly at around 15 mph wind speeds can reach over 75 mph.

FormationThere are many factors which cumulate to form a hurricane. Hurricanes form in tropical areas 23.5°North or South of the equator. They also need a sea with a depth of over 60m. Rising warm air triggers a decrease in pressure at higher altitudes. Warm air is under a higher pressure than cold air, so moves towards the area taken up by the colder, lower pressure air. The low pressure sucks in this warm air which then also rises. A continuous upflow of warm and wet air continues which leads to the creation of clouds and rain.

FormationAir surrounding the low pressure zone at the centre flows in a spiral. It flows anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere at speeds of around 75 mph. Air is ejected from the top of the storm, which can be around 15km high, and this air falls to the side of the storm away from the eye. As this process happens, it reduces the mass of air above the storms eye which causes wind speed to increase further. Not all of the ejected air moves away from the eye of the storm. Some cools and dries, sinking through the eye, increasing the low pressure at the centre.

Formation

As the winds pick up speed, the air pressure in the centre lowers, and the cycle continues. The hurricane will only grow in strength. As often seen from above, hurricanes are huge circular bodies of thick cloud, measuring around 300 miles wide. The cloud brings heavy rain, thunder and lightning.

End of the cycle

The centre of the hurricane is known as the eye, and it measures about 30 miles across. Often there are no clouds in the eye. From below it seems calmer, with a circle of blue sky visible above. The eye is formed because as it is the only area of the hurricane where cold air is descending. In the northern hemisphere, the prevailing easterly winds often steer hurricanes toward land. Despite this, a hurricanes course is often unpredictable. As hurricanes move inshore, their power reduces because their energy comes from sucking up moist sea air.