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That's the so-called "Roaring Forties":

"The Roaring Forties are strong westerly winds found in the Southern Hemisphere, generally between the latitudes of 40 and 50 degrees."

Which also raises the question about how the map projection / scaling affecs the percieved size and data layout.

Interesting. Does anybody know why it happens?

There is a continuous ring of ocean the whole way around Antarctica. That water can build up a lot of momentum as it is pulled around the Earth by tidal forces. At least, that's what the captain told me, I'm sure there are meteorologists around here with a much deeper understanding.