WEATHER REPORT: October 23

Thursday 23 October 2008

The fleet has broken free of the Doldrums and they are rapidly moving into the southern hemisphere.

As the southeasterly trade winds build, the boat speeds have come up, and everyone is looking ahead to their South Atlantic Strategy.

The southeasterly trade winds are much like the northeasterly trades.

These winds are driven by the pressure gradient around the large South Atlantic High. Only now that the fleet has crossed into the southern hemisphere, the rotation of the earth means that the circulation around the area of high pressure has changed direction.

The high still has anti-cyclonic rotation; however, the coriolis effect, an apparent deflection of moving objects, when they are viewed from a rotating frame of reference, means the high is rotating in a counter clockwise direction.

As a result, the fleet can expect continued SE’ly trade winds around the northern side of the high, transitioning to a N’ly flow as they sail south down the western side of the high.

While it might appear that a direct route to Cape Town, in the SE’ly flow around the top of the high, would be fast, this strategy never works.

This route would not only cause days of upwind sailing, but would also risk sailing into the windless center of the high. Thus the fleet will go west around the high, opting for more miles and a faster downwind route to Cape Town.

With good wind speeds expected, we should see the fleet cover a lot of distance in the next two days.