A satellite picture of a fully formed hurricane is a distinctive one. It is also a scary one for anyone who has lived through one. The central eye of clear air and the spiral of white clouds surrounding it are instantly recognizable. This view shows us the different areas that make up a hurricane.
A hurricane forms around an area of low pressure; the surrounding air rushes to fill this and is then forced upwards in a spiral pattern. At the top of the spiral some air is forced downwards through the centre towards the area of low pressure; this prevents the incoming air reaching the center of the eye, but most of the rising air is thrown outwards.
The eye is the circular center of the storm. It is an area of calm air and no clouds. The smoother the surface the hurricane is traveling over the more distinct the eye will be. The eye of the hurricane is usually between twenty and forty miles across, but may reach a greater size.
The air is clear and free from clouds in this area as warm air is falling, compressing and holding more water. It is an area of low barometric pressure. The winds of the eye are light because the wind from the outlying storm does not reach it, being forced upwards at the wall.
The wall of the eye, the division between the eye and the rest of the hurricane is the area of the greatest air movement, although high wind speeds will still be present away from the wall. At the eye wall air spiraling in from the outside of the storm is pushed upwards by the descending air of the eye.
In a large category five storm these winds will exceed one hundred and seventy miles per hour. The effective speed of the winds can be much greater on the side of the storm where the winds are traveling in the same direction as the hurricane is. For this reason there is a good side and a bad side of a hurricane to be on, relatively speaking. Areas to the north of a westward heading hurricane will sustain greater damage than those to the south.
The force of the winds are self perpetuating in the eye wall, the faster the winds are rising, the faster water laden air from the surrounding ocean must rush in to fill the gap, feeding more air and water into the system.
At the top of the column of spiraling air some air is pulled down the center of the eye by the low pressure, but most is thrown outwards at the top forming the distinctive spiral pattern of clouds we see on the satellite, called appropriately enough spiral rain bands. As these rain bands leave the center of the storm they cool and drop their moisture as rain. The air then sinks and is rewarmed by the sea, picking up more water and being fed back to the eye.
The total diameter of a hurricane is about three hundred miles, but can vary considerably from only sixty miles to over one thousand miles across. The diameter of a hurricane is no measure of its potential for destruction; Hurricane Andrew was a small diameter hurricane.
A hurricane once formed only breaks up if it passes over water too cool to heat more air to feed the hurricane, or the friction of a land mass causes a break in the wind patterns leading to an inrush of air to the eye. Large hurricanes can travel long distances over land before being completely blown out, due to the large amount of latent energy they carry.
