Henry Ambrose Hunt

“ The summer latitude is about 40° south. They are less extensive in summer than in winter, and do not so completely control our weather as they do in winter, for their southern position leaves room for the southerly extension of monsoonal low pressures, which make a great deal of our weather; but the anticyclone makes the change from hot northerly to cool southerly winds, the bursters of the east coast. ”

“ On the 25th September, the day following the gale, the weather everywhere was generally fine, while all that remained of the energetic high and low pressure systems were parallel isobars lying over the southern areas of Australia with very shallow gradients. This gale was very destructive and did much damage to property in Sydney; in some instances houses were unroofed, and the wind and sea on the coast were very heavy. ”

“ One of the most marked features of weather in Australia is the regular easterly motion of it in all seasons of the year, added to this the anticyclones—the controlling element in our weather—change with the sun, so that the latitude they follow in their easterly progress is further south in summer than in winter. ”

“ And just as the trade wind intensifies its northern circulation by adding force thereto, so the brave west winds of the southern ocean follow the general move of the weather systems northwards, and thus add force to the westerly circulation of the anticyclone, and its greater dimensions increase the size of the Λ depression, so much that it no longer has the sharply defined change from notherly to southerly winds, but from north-west to south-west winds ”

“ It is there explained that the south wind comes in front of an approaching anticyclone, and that it is felt from West to Eastern Australia, but it is only on the eastern coast, where, aided by the smaller friction of the ocean and the shelter which the mountains afford from other winds, that the southerly becomes more vigorous and rushes northwards in a squall, which happens so suddenly and with such force, that at times ships drag their anchors in Sydney harbour. ”

“ The energy of wind circulation increases over South Australia, and as the whole system moves bodily eastward from the Australian Bight to the mainland, the circulation is seen to be that of a fully developed cyclone of small area, with a diameter three to five hundred miles, formed out of the southern part of the extensive monsoonal depression. ”

“ When very strong the anticyclone is elongated and the southern isobars are flattened. (See Chart 30) . They are very cold and dry, having all the raw feeling of the easterly winds of England, and have been known to last for several weeks without intermission; they are the most persistent winds during our winter. In heavy westerly winds the cold is very severe in Bass' Straits, between the south coast of Victoria and Tasmania, rain, hail, and sleet being very common. It is almost needless to say that on land they bring very little rain, and they rapidly dry up the soil. ”

“ The warning of their coming is usually very short; it consists of a sudden increase in the sea on some northern part of the coast with wind from east to south, and falling barometers, while the high pressure over Victoria and South Australia becomes intensified and progresses into the Tasman Sea. ”

“ The south-east circulation about this anticyclone increases in force with the increasing barometric grade, and also by the wind circulation about the cyclone, and the effect of the two causes acting together is to produce a most serious gale. Rarely, these storms originate in a monsoonal depression somewhere over South Australia, which travelling eastward intensifies on the east coast. Heavy rain is a marked feature of these storms, but it is confined to the coast, and rarely if ever extends inland. ”

“ Its cause is found in an extensive col, the rear of one anticyclone being at rest over this coast, while another lies over the Australian Bight. If the grade is rather steep and the system at rest for several days, then the north-east wind persists with force proportionated to the grade, until the whole system moves forward; the southerly winds in the front of the approaching high pressure then displace the north-easter and the storm is over. ”

“ Their sphere of influence is very extensive, as may be noted in Chart 28, which shows rain over half Australia as the apparent result of this storm. Most of these storms take a direct easterly course over New South Wales and Victoria or through Bass' Straits. At times they move to north-east, the Polar winds being more energetic, and this feature intensifies all the storm and rain conditions. The winds in all these storms are violent, and in some very destructive. ”

“ 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 pronounced Australian weather chart No 20 March 20 1894
Australian weather chart No 21 March 21 1894 pronounced then has retreated, and is now only represented by one isobar, and where the western portion of the anticyclone existed on the 20th, an antarctic depression has protruded itself, and lastly an anticyclone is entering Western Australia. ”

“ The example selected and shown in Charts 6 and 7 took place on September 28th and 29th, 1892; on the 28th (Chart 6) , it appears that one of these storms had developed in the previous twenty-four hours, at the southern end of a narrow tropical or monsoonal tongue of low pressure. ”