Weather Preview for the La Transat en Double
by Tom Harrison, TH Meteorology 11 May 2021 21:09 BST
12 May 2021
La Transat en Double: Thursday 13th 0900 UTC: left ECMWF, middle GFS, right ICON. There is still significant spread in how the models are handling the developing depression on Thursday and the area of light winds ahead of this © TH Meteorology
While the crews of the Figaro 3s patiently await the passing of the latest in a string of powerful depressions, they will have their minds focussed ahead on what looks to be a difficult start to the transatlantic race. The course takes the double handed crews from Concarneau in northwest France, around the Island of La Palma in the Canaries, then straight across the Atlantic to St Barts. But it is the first 400 miles across the Bay of Biscay which look particularly tricky at the moment.
At the postponed start time of 1500 UTC on Wednesday, a stiff northwesterly will be affecting the Brittany coast on the western flank of this latest depression. The result will be an uncomfortable drag race for the opening hours of the race with crews tight reaching out into the Bay of Biscay in mean winds of 18-24 knots and short, 2.5-3.0 metre seas.
By the end of the first night the fleet will be hit with a challenging weather situation. A small, weakening depression will move quickly east out of the mid Atlantic through Wednesday afternoon, before deepening once more overnight into Thursday. This type of setup is particularly sensitive to small changes, and as a result there are significant uncertainties emerging in the various model outputs.
Although there is good agreement that there will be an area of light winds ahead of the developing depression, there is low confidence in when it will arrive and how long it will affect the fleet for. This is driven by differences in the depth and position of the developing low. Ensemble output shows that these differences are significant and result in a large spread in possible conditions for Thursday. These range from the fleet seeing a period of strong southerly or southwesterly winds following an area of complete calm; to the breeze remaining northwesterly right through the day and never dropping below eight knots. As such it is difficult to really trust any single output at this moment. Instead, the crews will need to prepare for a restless day with the potential for a lot of sail changes.
Tactically it is unlikely that this uncertainty will produce big splits in the fleet, but there is still the potential for correct fleet positioning to produce modest gains. It is marginal, but there may be a small advantage to being on the western side of the fleet through this transition as there is more support for the new northwesterly breeze to fill in first for those boats furthest west. However, there will be significant gains to be made for those crews quick to change modes as the system rolls over and this will be crucial regardless of fleet position.
After this complex situation, a much more consistent picture emerges. Through Friday morning the northwesterly breeze will gradually ease as a ridge of high pressure moves southeastwards towards Cape Finisterre. After the ridge axis passes over the fleet, the breeze will back southwesterly and then quickly increase through Friday afternoon. As a result, there will probably be a period of upwind sailing required in around 20 knots before the fleet round Cape Finisterre.
It seems likely that the first boats to round the cape will extend slightly as they turn southwards. The earlier boats can round the cape, the more they will be able to capitalise on sailing a more free angle south in the stronger winds before the breeze eases off through Saturday. Beyond this it should be a relatively simple passage around the Azores High, with generally northerly or northwesterly winds.
The transition into these more northerly winds has the potential to be quite tricky with a risk of another area of very light winds. Once the fleet are through these lighter winds, it should just be downwind VMG sailing in 15-20 knots of breeze as they make their way south into the trades.
So it seems that in typical Figaro fashion, the start of this race will greatly benefit those who are able to sleep less and perform quicker mode changes. For those crews which do this well and lead around Cape Finisterre, there is the potential to put a little bit of space on their competitors early in the race. Certainly, it will be an exciting couple of days to follow the race and see how the crews cope with this early challenge.
This forecast and preview is provided by Tom Harrison, TH Meteorology, email for more information.
More race information at www.transatendouble.bzh