Page:Types of Australian weather.djvu/22

18 centre is much steeper, and rain has fallen over the south coast generally and extended northwards almost to Central Australia.

On July 6th at 9 a.m. the weather chart presented the features shown in Chart 19. The cyclone has intensified all round, and has moved rapidly to the east, its centre is just entering Bass' Straits; very heavy gales from south-west are blowing in the rear of the centre; heavy rain is falling over Victoria and extends over the greater part of New South Wales. All the winds controlled by this storm were very heavy, and during the 6th July, as the storm passed through Bass' Straits, extremely heavy weather was experienced there. On July 7th it had filled up.

These occur during the summer months, and are most frequent in the western plains; they are developed in hot weather and in the low pressure known as a "Col" between two high pressures, when there is not enough grade to control the winds and the heating power of the sun is great; if to these there is added the presence of moisture from recent showers, we have all the conditions for the formation of a tornado. The force of wind is often sufficient to break off growing trees, two and even three feet in diameter, and the reason there is so little damage to life and property is not the want of power, but the sparse population and the very small number of towns.

Chart 20, March 20th, 1894. An extensive anticyclone lies south of Australia, giving way in its central parts to an extensive monsoonal dip. The isobars are generally uniform and of even gradients, though a suspicious interval exists to the west of New South Wales between the 30•0 and 29•9 curves. This is undoubtedly the area in which the secondary developed. Light rains were recorded in New South Wales and Victoria, but in Central Australia temperatures were high.

Chart 21, March 21st. A marvellous change has taken place. The area of high pressure on the previous day over the Tasman Sea has lost two-tenths in pressure. The monsoonal dip so