The frequency of tropical storms, be they hurricanes, typhoons or cyclones, peaks in the hottest season of the year in each region. The strongest winds, usually accompanied by torrential rain, are generally found about 25 miles from the centre of the vortex, while very close to the core, by contrast, the winds are light, and the sky is almost clear.
This latter region - normally about 15 miles in diameter - is called the eye of the storm, and can be spotted very easily nowadays on pictures from our weather satellites. But why it should be completely free of cloud is still something of a mystery to meteorologists.
As a first approximation, a cyclone is simply an intense depression, and in the case of ordinary depressions, the air spirals inwards and upwards towards the central core, rather like an inverted bath-tub vortex.
It is the ascending air, with consequent cooling and condensation, that lends to the depression its characteristic cloudiness to which we in Ireland are so well accustomed. Indeed this cloudiness, as we know, is particularly evident at the centre of the low.
Initially the formation of a cyclone over the warm ocean waters of the low latitudes follows a somewhat similar pattern. As pressure drops near the centre of the disturbance, the winds at sea level spiral inwards: the air approaching nearer and nearer to the centre increases its speed of movement to conserve angular momentum - in much the same way as a whirling conker revolves more quickly when its string is shortened.
But then there occurs a development unique to tropical storms: an "eye" and an "eyewall" form. The "eye" itself, as we have seen, is the circular calm and cloud-free zone, and the "eyewall" is a ring of thick, deep showerclouds surrounding the eye, and merging together to form what seems almost to be a solid, circular wall.
The existence of the eye has one obvious and inescapable implication: unlike a mid-latitude depression, a cyclone must have a zone of sinking, rather than rising, air at the centre of its vortex - a conclusion observations confirm.
This sinking air within the eye is subjected to higher and higher atmospheric pressure on its descent, and so becomes warmer and drier than its surroundings at each level; with no condensation taking place, no cloud exists.
But why do things happen in this way? As one expert on the subject has expressed it: "Theories on the mechanics of the eye's inception are still largely incomplete" - or to put it another way, it seems we simply do not know!