NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Southerly buster
From: Peter Fogg
Date: 2007 Jun 19, 20:51 +1000
From: Peter Fogg
Date: 2007 Jun 19, 20:51 +1000
Severe tropical storms are known in different geographic areas as cyclones (South Pacific), typhoons (Asia) and hurricanes (Caribbean), just different names for the same circular low-pressure systems that are born in warm tropical waters and, while rotating with great destructive force, move across sea or land slowly and unpredictably. As they cross land they tend to lose strength, although it is not unknown for them to veer back out to sea and regain ferocity. They are a feature of life in our tropical north, just as they are in other tropical areas. These days, the building code for constructions up there is supposed to ensure "cyclone-proof" buildings - as if there was such a thing. After every good storm there are examples of these rigidly reinforced buildings that have been destroyed, sometimes next door to somewhat more pliable old timber framed, corrugated sheet-metal clad shacks many decades old, that have seen more than their fair share of storms come and go. But I digress. While the effects of a good 'southerly buster' can be similar to those of a severe tropical storm, they are quite different weather systems. Sydney, at about 34 degrees south, is well beyond the tropical region. Southerlies are born out of depressions down in the Southern Ocean and make their way up the east coast of Australia as a cold front. They often create a dramatic change in the weather. They can be seen arriving as a boiling line of dark cloud approaching from the south, and in summer the temperature can drop from about 40 degrees Celsius (> 100d F) to less than 20 degrees (< 68d F) in a few minutes, as howling wind and strong driving, almost horizontal rain arrive. They can be quite brief - all over in a few minutes - or last for days. In summer they can create a welcome diversion on hot and sultry days; people talk about them 'clearing the air'. The weather bureau - as reported by some media, such as radio stations - tracks their progress and can predict their arrival at a given point with some accuracy. They tend to be a regular feature of the annual Sydney to Hobart ocean yacht race. The typical summer fine weather wind is a north easterly that grows in strength during the day, and throughout the afternoon can blow consistently at 20-30 knots. Before these winds the yachts fly to the south under spinnakers at a great rate of knots. But if a southerly comes up the coast mayhem results - sails are shredded, masts are broken and occasionally crew are lost overboard. It happens on a regular basis. The arrival of a southerly also tends to dash any hopes of making a record run to Hobart, as it can be very difficult to make any progress to the south while the wind blows hard from there. Navigation during yacht races these days is not so much about knowing the location of the vessel, as that is a given (all that individual boats, or anyone else for that matter, have to do is go to the official race website where the position of each of the yachts is updated constantly and displayed in real time). No, the real task of the navigator is to know where the boat SHOULD be, in order to minimise the effects of unfavourable weather systems, as one example, or maximise the effects of the favourable current, for another. I've always thought of southerlies as being part of summer weather, although the recent severe storms from the south (another is expected in the next few hours) have happened in winter, which is normally a fairly dry period here. Strong dry winter winds normally come from the west, the 'winter westerlies'. We think of these as being safe winds that are easy to sail to, as the boat is often on some sort of beam reach sailing up or down the coast, while the wind does its best to push the boat away from the coast. The sailor feels encouraged to hug the shore, which makes for a more interesting passage, although it does tend to be a cold run. Although the effects of the recent storm that pushed the Pasha Bulker onto the coast were fairly devastating, widespread rain has been falling in parts of Australia that have been in drought for years, so not entirely unappreciated. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---