There is three names describe one of the most powerful forces in the nature. Which terms is used depends on the part of the globe they are located. In the Atlantic they are hurricanes, in the pacific they are typhoons , whereas in the Indian Ocean they are cyclones.

Satellite image of hurricane

How this phenomenon occurs: we have warm moist air rising from the seas around the equator and travelling towards the pole. Factors such as sea temperature, the Earth’s rotation and prevailing winds affect the movement of moist air. If particular set of factors come together over the Oceans at the equator, vast amount of warm moist air accumulates and this builds into the extremely powerful storms we call hurricanes, typhoons and cyclones.

Earth’s rotation


the Ocean

Studies confirmed scientists that the sea temperature must be at least 26°C. Scientists guess is that by observation of the sea area around the origin of hurricanes the one factor that always contributed was this minimum sea temperature. Using what you know about temperature and moisture it is easy to work out that the air above the warm sea gets heated and vast amount of water evaporates due to the capacity of warm air to hold this moisture. This mass of moist air raises rapidly, begins to cool and as it does so, forms clouds.
A consequence of the rising moist air is that because it is rising very quickly it creates an area of low pressure at, and above sea level. Here are a couple of common experiences that may help explain why this happens: when you drink a liquid through a straw the common expression is that you are sucking up the liquid. There is no actual force of sucking, what are doing is creating negative pressure from the top of the straw and it is air pressure that pushes down onto the surface of the liquid and forces it up the straw towards the negative pressure.
As a living organism on Earth’s surface, we have evolved under the force of atmospheric pressure and are not normally aware of it as we go through our daily lives.
On occasions we do have become very aware of it, as you will understand from this second common experience: on rail station platform that have high speed trains passing through, there are warnings to stand back from the edge of the platform as there is high speed train approaching and often there is a line for you to keep behind. The reason is that although most people think that they might be sucked on the track if they are too close, the high speed train is moving so fast that a large amount of air is being pushed in the front of the train and this create an area of high pressure in front and lower pressure along the side of the train. A partial vacuum runs along the side of the train.
The lows of physics dictate that these areas of high and low pressure cannot exist beside each other and air has to move from the higher pressure to the lower pressure to equalize the overall pressure. The faster the train moves the greater the difference in pressure and the faster the air moves into the lower pressure area. Pressure from the movement of air by a high speed train is easily enough to dislodge the human body from the standing position, and of course you will head in the direction of the low pressure area on the track. By the way, the same applies to trucks flying past you on a motorway so be aware of this also if you have to stop on the hard shoulder.
Back to the hurricanes where we have a mass of moist air travelling at high speed upwards, with low pressure underneath. Now you can see that due to air pressure, the surrounding air must rush into the low pressure area and this is drawn across the sea towards the center of the newly forming hurricanes. The air becomes heated and loaded with moisture and heads upwards. As you now know, this moist air will cool as it rises causing the water vapour to condense, form clouds and as the mass of cloud accumulates, at some point we have rain.
The clouds and rains are pushed outwards by the rising air around the middle of the hurricanes and the cooler air assists in pushing more air at sea level towards the center of the hurricanes. So we have a cloud generating cycle that will continue so long as there is a source of warm moist air at the center.
Other key factors come into play now. Rotation of the Earth and driving prevailing winds cause the mass of rising, warm, moist air to spin and moves across the sea. The one common experience that comes to mind is water going down a plughole: gravity is a force that pulls things straight downwards, but water does not simply disappear straight down the plughole. The fluid water is affected by the rotation of the Earth and this causes it to spin down the plughole. The situation is very similar with the mass of rising moist air, and that is why hurricanes and cyclones spin anticlockwise in the northern hemisphere and typhoons in southern hemisphere spin the other way round.

southern hemisphere

There is no upwards movement of air in the eye of the hurricanes and clouds do no form here. The rising, warm, moist air forms the wall of the eye as the high winds known for there destructive force, spin around the outside.
So the basic driving force hurricanes, typhoons and cyclones is water vapour. As long as these storms are travelling across the sea water, they have a source of water vapour that sustains them and has the potential for increasing their force. May be you remember a few occasions hearing in the news that hurricanes weakened a bit when hitting the Caribbean Island or Mexico then travelling into the Gulf only to increase in strength before hitting Florida or the other southern United States.

Caribbean Island


New Mexico sunset while storm

When storms hit land, their source of energy is cut off and they weaken as their cloud generating cycle is cut off. Unfortunately for those individuals caught in the storm’s path, not only are they battered by strong winds, but the storm also dumps its water vapour as rain and this cloud amount to several billion tons of liquid within a short period of time.
Will global warming increase the frequency and strength of these storms? I don’t know anybody knows for certain. The occurrence of storms depends on many different factors such that they can’t be predicted. Therefore we can only hope that a temperature increase alone may not lead to an increased frequency. 



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