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    Southerly buster
    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.
    
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