Page:Hunt - The climate and weather of Australia - 1913.djvu/144

Rh. 119 120.

Willy-willy affecting Coastal Parts only.—The tropical cyclones, which during the summer half of the year are occasional visitants to the northwest coast of West Australia and known there as "willy-willies," generally follow paths tending to carry them inland. But in most cases their identity is then speedily lost, barometric intensity and wind energy disappearing and the storm becoming merged into an ordinary "monsoonal dip." In a few cases they keep out to sea, and, moving southwards, may even round Cape Leeuwin. In the case of the very violent one shown centred near Onslow on the 7th February, 1911, apart from the heavy local coastal rains of the 6th and 7th, the rest of the State did not benefit, and the storm either moved off seawards or broke up altogether.

. 121 122.

Willy-willy moving Inland.—On the 19th January, 1909, is another willy-willy not quite so intense as that of the 7th February, 1911, but occurring with almost the same general pressure distribution. Yet this one moved inland, and by the 21st January had reached the Murchison gold-ﬁelds, having lost but little of its intensity, and bringing very heavy rain to the Murchison and Northern Coolgardie gold-fields. It then moved slowly eastward across the continent with diminished intensity, but still accompanied by rain even to the Queensland coast.

. 123 124.

Gales through Bass Strait.—Westerly gales naturally occur whenever the barometric fall southwards is rapid and the isobars lie approximately east and west through the strait. The most frequent cause of this is the passage of an Antarctic low, not only intense but on a large scale over Southern Tasmania or the ocean waters south of it. Such is the storm shown on the charts of 13th and 14th September, 1912. The chart of the 13th shows what may be described as a "square-headed" low, the squareness being due to the formation of a second trough closely following the first. Such a development in an energetic disturbance invariably means severe weather, especially along the coast line, with hail showers and not infrequently thunder. The weather of the 13th was no exception. The first eighteen days of this month were exceptionally boisterous, owing to the prevalence of this type of storm.