The Vendée Globe is the world’s ultimate race course: one non-stop lap of the globe. The course starts in Les Sables d’Olonne on 10 November. There are three marks of the course – the Cape of Good Hope, Cape Leeuwin and Cape Horn – all of which must be rounded to port, before finishing back in Les Sables d’Olonne.

Beyond these marks we skippers must choose our own way around the world and that navigation will be primarily defined by weather rather than geography.

Over the next three issues I’ll walk you through the three major sections of the Vendée Globe course, and give an overview of the key weather features which will challenge, punish and reward every skipper in equal measure as we race, for up to three months, single-handed, non-stop, around the world.

First we look at the Atlantic descent, crossing Biscay and the ‘Pot au Noir’, before entering the southern oceans.

Atlantic descent

Leaving the north Atlantic in late autumn is seldom a relaxing affair, but the early stages of this route are often trodden by the IMOCA skippers who are well versed in transatlantic ‘sprints’. The course down the Atlantic can be split into defined phases, each governed by specific weather features. However, when navigating a boat capable of easy 500-mile days, our focus must be split, also paying attention to the development of weather features two, or sometimes three, steps ahead.

The start of the race will be intense, skippers needing to manage boats at their heaviest, laden with food and spares. The fleet will be close, and technical problems should be limited, which means fast racing. In a class where speed differentials can exceed 20 knots, risks or mistakes can be punished hard and boats getting ahead early may stay that way for the entire race.

Exit from Biscay

The earliest routing decisions will be the only ones skippers are allowed to make in collaboration with their shore team, as they’ll be made on shore in the days before the start. Some skippers may even delegate total responsibility for the initial few days of routing to a meteorologist – freeing up headspace to deal with the emotion and energy required to start the race.

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We can expect a routing made before the start to be accurate for 48 hours, but from the moment the gun goes we are alone in our decision making. The rules of the Vendée Globe race do not allow outside assistance on any matters relating to performance or navigation.

Typically, an exit from the Bay of Biscay will involve crossing a cold front within the first two or three days of racing. In this scenario a front advancing across Biscay will bring headwinds in the south-westerly sector ahead of the front, with a north/north-west shift after it has passed, which will propel boats quickly south.

Crossing the front, we’ll need to be mindful of sea state (boats are often forced to return to the start after damage crossing these first fronts), to monitor the speed of the front and make a judgement on how far west to push before crossing it. Any investment to the west could pay dividends later on.

The Azores High

Every skipper will have been constantly observing the position of the Azores High during the build up to and following the start of the race. The position, shape and stability of this high pressure system will dictate how easily or quickly the fleet will transition to the north Atlantic trade winds.

A stable high pressure situated over the Azores will open a route directly south, along the Spanish and Portuguese coasts. High pressure in the east or moving east will force boats out to the west and a developing low pressure around the latitude of the Canaries will also push boats west.

At this stage skippers in faster boats should be already making decisions about where to cross the doldrums, always trying to bank miles to the west in the most advantageous winds.

Atlantic Islands

The Atlantic Island archipelagos of the Canaries and the Cape Verdes offer both risk and potential rewards on the route south. The wind accelerates between the higher islands, providing an expressway south to boost speed. Each island also casts a wind shadow, however – the effects of which can be felt up to 80-90 miles downwind.

As a solo sailor the added risks of passing through island chains, closer to the shore and with additional traffic, must not be overlooked. Wind shadows can be well mapped using satellite images, ASCAT files and GRIBs.

Trade winds (North)

The strength and extent of the trade winds will be determined by the position of high pressure in the North Atlantic and the position of the doldrums. The less established the high pressure, the weaker or further south the trades will be, making progress to the south slower.

In typical conditions trade winds will start around the latitude of the Canary Islands and from the north-east, veering east the further south you go. At this stage it is hard to make ground to the west without losing out big miles to a close competitor heading south. We will need to be sure of where we want to cross the doldrums and gybing in the trade winds to make a westing should be carefully considered, along with making the most of advantageous or temporary shifts in the wind direction.

Special attention is required late afternoon and early evening to watch for squalls, created by damp, hot air rising during the heat of day. Satellite imagery is used to understand the volume and likelihood of squalls, while radar can be used during the night or when not on deck for early detection of clouds.\

The Doldrums

Officially this area is named the Inter Tropical Convergence Zone. It is the band of low pressure which runs around the centre of the earth, close to the equator, flanked either side by trade winds. The doldrums in particular refer to the windless areas within this zone which can make or break early positions within the race.

The doldrums are normally shaped like a triangle on its side, with the base to the east of the Atlantic and tip to the west.

The further west a sailor is able to make their passage into the South Atlantic, the less distance they should have to travel across the doldrums.

The longitude at which a competitor crosses will be pretty much determined by the time we have reached the Cape Verde latitudes, and any early banking of miles west could pay dividends at this point.

Once entering the doldrums, the main objective has to be a route south to the new trade winds. Clouds and electrical storms will punctuate local navigation; satellite imagery and radar once again play a key role in local tactics. Modern GRIB files are now pretty accurate at showing the doldrums, and satellite imagery will also give good real-time confirmation.

The South Atlantic Trades

Driven by the position, stability and size of the St Helena High, the trade winds in the South Atlantic mirror those in the northern hemisphere, starting easterly close to the equator, then gradually backing to north-east.

Though the first ‘mark’ of our course is the Cape of Good Hope to port, we will be forced to the west Atlantic to find the fastest route south – a route to the east will be against headwinds.

If the St Helena High is situated in the central South Atlantic, boats may find a course further east that allows them to play with the gradient breeze around its centre. However, should the high pressure be weaker, or further north, boats may seek to benefit from both the current and the thermal breezes along the Brazilian coast.

The usual precautions around squall activity will be important. In this part of the race foiling boats can be expected to benefit from fast reaching conditions.

With eyes forward, skippers will have been paying close attention to the development of South Atlantic low-pressure systems over the previous week, looking for the fastest strategy to jump the train to the south.

The Semi-Permanent Cold Front

This is a weather feature which extends from just south of Rio de Janeiro south-east into the South Atlantic. The front is formed between two areas of high pressure in close proximity that create a huge weather front – which in turn generates young low-pressure systems that slingshot their way to the Southern Ocean.

A dream scenario would be to arrive at the semi-permanent cold front ahead of a developing low-pressure system with its own cold front, which will then provide northerly winds and fast reaching conditions towards the south-east.

This is another point at which the fleet will separate. Those who get the timing completely right have completed the South Atlantic and can gain hundreds of miles on a boat that arrived just behind a developing front.

Should the expressway south not be open, boats will either choose to play further with the St Helena High pressure – making their way east by sailing in towards the centre of the high then gybing back out before the wind speed drops too much – or they may choose to continue south looking for an older depression coming from the tip of Cape Horn to ride east.

The temperature will change dramatically at the semi-permanent front as warm and cold air masses collide. The change from shorts and T-shirts to full thermals and woolly hats could be as quick as 24 hours.

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