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Downwind in the Southern Ocean

For a hardy crew in the vicinity of Kerguelen Island
it is a matter of get in, sit down, shut up and hang on!

 After the second grueling leg of the 1997-'98 Whitbread 'round the world race, wet and weary crew stumbled off their foxy Whitbread 60s to enjoy the warmth and vitality of Perth, Western Australia.

The race leaders had left Cape Town, South Africa just two weeks prior and experienced the whole gamut of Southern Ocean effrontery - from blinding snow squalls and surfing speeds in excess of 30 knots to the ridiculous calm of a 'roaring' 40s high pressure cell. Even the albatross and giant petrel couldn't get their wings in the air during that one!

But one thing lingered in the minds of those who had experienced those wicked snow squalls and it had something to do with feeling out of control.

Andrew Cape, navigator on Toshiba, told it like this:

He and the rest of the crew were sailing further south than the rest of the fleet immediately west of Kerguelen - the half-way point of the Indian Ocean leg - when gusting winds from the north east signaled the arrival of the next low and its associated frontal system.

Toshiba had no choice but to surf downwind, with the building northwesterlies, sailing into the throat of the Southern Ocean beast.

Because lows south of the equator spin clockwise, winds are sucked into the centre of the storm first from the north-east, then north-west along the frontal cloud band before they suddenly, and swiftly, change to the west, south-west. At this point, the 'front' has passed.

"You know (the westerly change) is coming," said Andrew, "but you never know its strength."

In this case the barometer dropped to 980mb before the westerly change struck Toshiba and she jibed to sail north. Only then did the barometer begin to rise.

"We were worried as the boat ran south, that we would run into more wind, but there was nothing to do but sail downwind in those conditions," Andrew said.

The change brought 35-40 knot winds for the next three days and Toshiba surfed downwind towards the north-east almost keeping pace with the Southern Ocean storm.

  Tips from Andrew Cape:

• Lows in the Southern Ocean (and everywhere else outside the tropics) develop at the 500mb level (about 20,000 feet) and come down to the surface as they mature.
• The same storm will decay from the top.
  "If it stalls ( a kink in the jet stream at the 500mb level and above is a good sign that weather systems will stall at that point) then you know the storm will start to decay," says Andrew.
• While the general rule of thumb dictates that winds will shift from north-east to north-west before the onset of a westerly change (again, this pertains to lows south of the equator. To the north think south-east to south-west before a north-westerly change) this is not always the case. Sometimes a smaller low will rotate around a larger low creating brainteasers for navigators aboard ocean racing yachts.
• The one predictable thing about the Southern Ocean? It's not so predictable, says Andrew!

© Jamie Brown/weather-wise.com 2000

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