What causes a hurricane to form?

Question

And what are the "symptoms" of a hurricane (like high winds, howling winds, etc.)

Answer 1

A hurricane forms when waves of weather come off the west coast of Africa. As they make their way across the Atlantic (guided by the trade winds) they sometimes organize into low-pressure systems. Low pressure systems naturally spin counterclockwise (due to some physics). This causes the air in the middle to rise, and draws more in from the outside, making the storm stronger. Since in the open ocean there is nothing to get in the way, the storm will continue to strengthen as long as there is a nice supply of warm water to feed it (more than 26 celsius).

A landfalling hurricane is characterized by very strong winds, but more importantly rain and flooding. Flooding causes far more damage in hurricanes than wind does. Partly from the rain, and partly from the incoming waves from the ocean as the hurricane blows the water onto land.

Answer 2

To the excellent answer from Scott Evil, I will only add the following.
A hurricane, a tornado, a low pressure or even a local thunderstorm are all the same: convective depressions. It needs first warm at the bottom, and cool upward. It works then like a chimney, bringing air upward and creating a lower pressure as it rises.
A hurricane is the name given to tropical storms above the Atlantic. As said, it needs sea temperature above 26°C. The wind around any depression turns counter-clockwise in the northern hemisphere but clockwise in the southern hemisphere. It is due to a combination of the Coriolis effect, due to the earth's rotation, and the centrifugal effect of the rotating air.
An interesting question then is: What happens when the depression starts right on the Equator? Well, the situation is said to be unstable and it will eventually move south or north and gain momentum.
That, combined with the fact they are growing under the Trade Winds make the Hurricanes to grow stronger as they move west and north.
The 'fuel' of any depression is humidity because if dry air cools at the average rate of 1°C per 100 meter by adiabatic effect, saturated air - as when clouds are formed - cools only 0.5°C per 100 meter. The reason is that in order to condensate from gas to liquid, water needs to release energy in the form of heat.
The result of it is an even increasing effect of the convection and the rising of the air.
Given enough warm moist air under cooler air, you will get a 'chimney' that goes all the way up to the tropopause, the limit of our 'weather' atmosphere, at about 38,000 ft of altitude. That is what happens in a thunderstorm.

Answer 3

You have asked a very good question. It is the energy from water vapor that is theessential element in the genesis and sustenance of a tropical storm. What we first see in the development of such storms are large unorganized areas of convective clouds which I have termed Convective Cloud Clusters. These are the incipient areas of storm development. The first thing we need to see for a storm to become organized is ocean surface temperatures of at least 28C. As clouds then begin to grow, water vapor is condensed due to the lower pressure aloft and this releases a considerable amount of heat energy into the atmosphere and as long as there is no mechanism aloft such as strong shear (differences in wind direction and speed) which can remove this heat the surface pressure will begin to drop. At this point another very important ingredient is necessary and that is southwesterly winds to the south of the cloud cluster which is embedded in the trade winds (easterlies). This wind structure leads to a counterclockwise or cyclonic circulation which brings surface air filled with water vapor toward a developing center of low pressure and circulation. This air then rises in the convective clouds and further supports the development of low pressure. Soon the cluster becomes a tropical depression, the first real stage in tropical storm life cycle. It is numbered at this point and aircraft flights are made into the depression for close up measurements by dropsonde instruments to record temperature and pressure down to the surface. The initial discovery of the storm is generally done by satellite data interpretation, but satellite data will be closely monitored throughout the life cycle of this storm. As the storm develops it next becomes a tropical cyclone and is now given a name. It may also develop an eye (about 25% do at this point in their history). The final stage of the storm is the hurricane. Throughout the life of this storm water vapor is "the" source of energy that is crucial to its life cycle so that when the storm finally moves over land and that energy source is cut off, the storm immediately begins to dissipate. The major damage from hurricanes is the surge or wall of water which precedes the arrival of the storm. This causes flooding especially if it coincides with high tides. Secondly there are high winds of course which generate flying objects. There are also severe thunderstorms with lightning and quite possibly a tornado. You should always listen to the authorities and evacuate if requested or ordered to. It is a good policy to be as far away from an arriving hurricane as possible. Hope this helps and if not then let me know.

Answer 4

Your question has been nicely explained by the above three persons.I will summarize it and give below the conditions required for the formation.
(1)A pre-existing near-surface disturbance with sufficient vorticity and convergence is required in the initial stages of the formation.In the case of the hurricanes ,low pressure systems form from the waves of clouds that come from Africa.
(2)Warm ocean surface(atleast 26.5 degree celcius) upto a considerable depth(atleast 50 meters).Because developing hurricanes gather heat and energy through contact with warm ocean water and the addition of water vapour by evaporation from this water surface powers the hurricane like a heat engine.
(3) Moist atmospheric layer to a consierable height(atleast 5 Kms).Because dry mid levels may prevent convection activity.
(4)A minimum distance (atleast 500 Kms) from the equator so that coriolis force can act on it to introduce the revolving motion.Over the equator the coriolis effect almost vanishes.
(5)Vertical wind shear should be less.Otherwise it will disturb the system.
(6) Steep lapse rate so that unstable condition will be there to aid strong convection.