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2010/02/01-07h08
Cape Finisterre
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| The NW tip of the Iberian peninsula has a terrible reputation. Exposed to the Atlantic, this jagged coastline provides little
shelter whilst the weather conditions can change extremely quickly. With a zone of high pressure forming over the South of
the Bay of Biscay, Groupama 3 will have to pass very close to the lighthouse, which marks the most western tip of Europe...
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A compulsory passage for all vessels setting out from Northern Europe bound for the Mediterranean, the Atlantic islands
(Azores, Madeira, Canaries, Cape Verde), the West Indies or South America, Cape Finisterre marks the boundary between two
different ocean systems as well as two different weather patterns. Indeed, on the one hand the Azores High extends its way
out here at varying degrees of intensity during the summer months, whilst in winter, it's the Eurasian Continental High which
settles here while leaving the door open to Atlantic lows moving across from Newfoundland. In this way the periods where there
is a change of season (spring and autumn equinox) are often the site of rapid changes in the weather and violent gales, as
this steep coast acts as a continental buffer against the Atlantic air flows.
Furthermore the relief of the sea
bed associated with the general and tidal currents cause the sea to pick up to what can be a dangerous level at times as the
continental shelf isn't very broad. As such it's a fairly common occurrence, between the headland of Estaca de Bares and Cape
Finisterre (which amounts to around a hundred miles) and across a band of up to forty miles or so from the coast, to witness
very confused seas, with the wind strengthening by 2 to 3 levels or more on the Beaufort scale, whilst conditions will be
fairly calm in the Bay of Biscay or the Atlantic Ocean.
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Climatic rampart
The Iberian peninsula forms an effective barrier between the Atlantic Ocean and the Mediterranean, with the Pyrenees extending
out to the foothills of Cantabria, Asturia and Galicia to its North. This high ground bordered by cliffs forms a divide between
the oceanic and continental systems, as well as between the zone of subtropical high pressure and low pressure from the temperate
regions. This greatly influences the climate around the Cantabrian coast, which is both mild and very wet. Yet the average
atmospheric pressure is high (average value between 1016 and 1020 hPa), especially in winter with the Eurasian high settling
over the area. The upshot of this is considerable variation in the weather conditions, especially with Spain being under the
influence of four large air masses:
- the continental polar air from Eastern Europe is dry and stable, characterised
by the winter months where the temperatures are colder with N to E'ly winds.
- the continental tropical air from
North Africa is dry and stable, characterised by the summer months where the temperatures are hotter with E to S'ly winds.
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the oceanic tropical air from the Atlantic is hot and shifty and laden with humidity, characterised by large levels of
cloud cover, mild weather and S to SW'ly winds.
- the oceanic polar air from the North of the Atlantic is cold
and shifty and laden with cumulus, causing high levels of precipitation in squalls, associated with violent W to NW'ly winds.
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A marked contrast
In this way, in summer there are prevailing N'lies which tend to follow the contour of the relatively high coastline, from
200 to over 500 metres between Cape Ortegal and Cape Finisterre. As such, the breeze clocks round to the NE between La Coruña
and the Spanish headland, filling in along these cliffs and as far as 40 miles from the shore. At that point the weather is
clear, visibility is good to excellent, though a morning mist can hang around the bottom of the bays (La Coruña in particular).
Thermal breezes are very common during this period and the sea breeze (day) is more pronounced than the shore breeze (night).
It also tends to increase the synoptic wind since it blows in from the N or NW.
In winter the Atlantic lows whip
along the Iberian coast and the winds are predominantly SW to NW'lies. In general, the breeze initially blows in from the
South for a day, with heavy rain and low cloud, before clocking round to the SW for several days. It gradually veers rounds
to the W then the NW as a cold front sweeps through with violent squalls and rather cool temperatures. If the wind only eases
for a few hours without veering round to the N and then the NE, this means it will back round to the SW as it builds, with
another low or associated cold front on its way. This type of weather can last several weeks with rare interludes, which can
hold a sailor up: this is why there hasn't been an opening for the past three weeks... However, for Groupama 3's attempt on
31st January, Franck Cammas and his crew will have to negotiate a transition phase. The reasons for this are that behind the
cold front, which enabled them to set off from Ushant at midday on Sunday, the zone of high pressure is reasserting itself,
incurring a large zone of light winds for several hours...
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Heavy traffic
About 370 miles from the Raz de Sein, Belle-Île or La Rochelle, Cape Finisterre forces the navigator to sail along the Spanish
coast for nearly a hundred miles if the aim is to follow the shortest route. In fact the continental shelf, defined by shallow
waters measuring up to just 200 metres in depth, isn't very developed since it stretches just twenty miles or so and shelves
off steeply to 3,000 metres less than 40 miles from Cape Finisterre or the Pointe Estaca de Bares. On the other hand, between
these two reliefs, the sea bed doesn't shelve quite so steeply and several banks contribute to making what is often a confused
sea, even in calm weather.
A passage around Cape Finisterre is compulsory for ships coming from Africa or the Mediterranean
bound for the English Channel (or the reverse): the shipping heading up sails along a lane just 10 miles from the Spanish
coast, whilst the shipping heading down is 20 miles off. The amount of shipping is particularly intense and it shouldn't be
forgotten that there are large numbers of fishing boats off La Coruña and to the South of Cape Finisterre. A route hugging
this headland is often excellent, especially in a moderate N'ly wind, as the sea becomes calmer and the wind less violent
the minute Cape Finisterre is rounded. A constant watch is required however.
The Bay of Biscay offers little shelter
along the Spanish coast in a W to NE'ly gale, especially between the Franco-Spanish border and Cape Finisterre. As such great
caution is needed on the passage around the NW tip of Spain, even when the wind and sea conditions in the Bay of Biscay are
calm, as it's extremely rare to make the rounding scot-free. In any case, you can expect a notable increase as well as a shift
in the wind, as the jagged coast still causes the breeze to be deflected about forty miles or so offshore. In this way the
W'ly wind backs round to the SW as you close on the coast between Villano and Estaca de Bares, and the N'ly wind veers round
to the NE, returning to form once Cape Finisterre is in its wake. Navigators also need to watch out for the very violent storms
which are created close to shore. The same is true in relation to the fog which can conceal the land, even in fine weather...
Dominic Bourgeois
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