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Developing low pressure may ease leaders slide into the deep south Leading skippers in the Vendee Globe
have been waiting for an opportunity to 'cut the corner' of the December 1, 2000 Since the leading skippers entered the south east trades one week ago, they have been sailing the long way to the Southern Ocean: Around a great balloon of sub-tropical high pressure called the St Helena High. With the windless centre of the high hanging around the western side of the South Atlantic, there was no choice but to 'go with the flow' and sail around - first to the south west, then due south and now leader Yves Parlier is beginning to head south east as he crosses latitude 35 degrees south. Now, at long last, the leading yachts may be able to grab a favourable wind flow as low pressure develops to their south west. This low and its associated front are pushing strongly into the St Helena High, skewing it in favour of those leading yachts, as they will now be able to sail downwind on a south east heading - sailing for the Southern Ocean and her constant westerlies, while at the same time heading on a course that removes miles from the ultimate finish at Les Sables D'Olone, rather than adds them on. This fortunate position for the leading yachts may prove the be the downfall for those yachts only a few hundred miles behind. There is a real chance that the leaders can 'cut the corner' of the St Helena High, while those behind may miss the window of opportunity all together and get caught in the centre of another eastwards-moving sub tropical high. Such a scenario would place the leaders further ahead by leaps and bounds, and it would be very doubtful if those in the second pack would ever make up the ground. © weather-wise.com 2000
Animated loop of South Atlantic
surface pressure Image courtesy of OceanWeather In these three frames, you can see the St Helena High forced to the east by an emerging low pressure cell off the coast of Uruguay. By frame three, the front associated with this low has created a 'ski-ramp' of isobars, with winds blowing to the south east as the low to the south west squeezes the St Helena High to its north and east. Behind the front is another balloon of high pressure. If skippers in the second pack miss the favourable winds associated with this front, they will lose even more miles navigating through the light airs behind this wind band.
Fleet positions This image shows more clearly how the leading yachts are heading south east under the St Helena High. To their south a low pressure cell is developing and if it deepens, the westerly winds circulating over the top of it, will push them quickly into the stream of consistent westerlies below latitude 40. Picture courtesy of Virtual Spectator. Explore comment from the November 30: In order to avoid the light winds of the Saint Helen high
pressure system, the international fleet of the Vendée Globe 2000 has made its
rapid descent of the Southern Atlantic through a very narrow wind corridor
between 27° W and 30° W. Right now, the skippers will be watching their
barometers, as the first sign that they are approaching the centre is when the
pressure gauge increases. The fleet will be careful to stay at a distance from
the calm airs circling the central zone of the high pressure, and yet will need
to find a way past, which means making a fair compromise between heading and
speed. As soon as the boats have got past the heart of the anticyclone in
latitude, the winds will swing from North to Northwest. |