How the America’s Cup weather favours Team New Zealand

INEOS Britannia’s Tom Cheney analyses the conditions the America's Cup teams can expect and how that has affected the teams’ design strategies

The Louis Vuitton Challenger Series kicks off at the end of August and runs through to late October. Why so long? Well, the addition of two more teams compared to the previous America’s Cup means an extra round of the Challenger series. All six teams, including the defenders Emirates Team New Zealand, will compete in the round-robin stage before the first Challenger is eliminated. The remaining four then battle it out in two knockout stages.

The length and timing of the Challenger Series adds a unique element to the design challenges of this America’s Cup. It wouldn’t be too cynical to suggest this was likely part of the cunning Kiwis’ defence strategy.

The Challenger rounds take place in August and September, when Barcelona typically sees more consistent thermal winds, usually with predictable patterns, and moderate sea states. Then the America’s Cup Match in October brings increased variability with a mix of weaker thermal winds but potential for stronger gradient winds, and a significantly worse sea state.

This difference in expected conditions requires the Challengers to design versatile boats capable of performing well in the more predictable moderate September conditions, while the defender can prepare specifically for October, which has a less consistent, but higher average wind speed (depending on time of day) and much more significant wave height.

Here are the conditions we might expect to see as the event unfolds:

August/September

Dominant winds – The synoptic summer wind over Spain is generally from the north-west. In Barcelona this is almost completely blocked and bent by the Pyrenees mountains. Instead, the Garbí wind, a thermal breeze from the south-west, is prevalent during the summer. It typically starts at 10-15 knots in the early afternoon, increasing to 14-18 knots mid-afternoon.

Sea State – 0.4-1.5m swell from offshore.

Other winds – South-east gradient winds struggle to reach the coast directly, resulting in lighter breezes. Easterly winds can bring larger swells (1-2m) if moderate, but often get diminished by the thermal effects if light.

Temperature – Longer daylight hours and warmer temperatures can enhance thermal wind patterns, making the Garbí more consistent and predictable.

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October

Dominant winds – The thermal influence of the Garbí diminishes as the temperature drops. Generally this leads to lighter south-west winds. However, the Garbinada is a stronger south-west wind, driven by westerly component gradient wind. This synoptic wind parallels the coast to become south-west or south-south-west. These windier days may bring up the average wind strength.

Sea State – Increased Mistral conditions in southern France cause significant waves which can present in Barcelona as 2-3m swell. This accompanied by south-west wind can cause uncomfortable, tricky conditions.

Temperature – Cooler temperatures reduce the strength of thermal winds. There is a higher likelihood of northerly gradient winds bending around the Pyrenees, leading to more days with east-south-east or even north-east breezes.

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