XXL storm bearing down on Europe's western coasts
To date, autumn in the North Atlantic has been predominated by hurricanes tracking offshore from the North American mainland, however later this week a significant low pressure system will sweep south from Greenland and impact every west-facing coastline in Europe.
The storm is set to rival ‘Hercules’, the low pressure system that struck Europe in early January 2014 and initiated the protocol of naming significant mid-latitude storms. Hercules is also remembered as the storm that saw Jamie Mitchell launch an aborted mission at huge Belharra.
The storm, yet to be named though it will be 'Aiden' if it meets the threshholds, will form later today when the remnants of three low pressure systems: Hurricane Epsilon, the tenth hurricane of the Atlantic season; plus a deep low pushing off the Canadian shield; and a very large low centred south of Iceland, begin to merge into one system.
By Monday night the three systems will have consolidated into one, forming a storm that spans the North Atlantic, stretching from the Irish west coast back to Greenland and north to Iceland. The storm is then forecast to bomb, meaning to drop more than 24hPa in 24 hours, before reaching maximum intensity with a barometric pressure of 939 hPa, wind speeds of 65-70 kts, and Significant Wave Height of 66 feet, directed west towards the Irish coast and southwest towards the Bay of Biscay and Iberian Peninsula.
The swell will reach landfall the next day, Wednesday, with Mullaghmore breaking in excess of 35ft, however with the wind forecast to blow at 30kts from the west-southwest it may be coming around the corner more than is ideal forcing Irish surfers into even more protected nooks.
The swell will next reach the Bay of Biscay by the next day, Thursday, coinciding with a weak ridge that’ll see winds swing from westerly to light south-east and perhaps even light north-east later in the day. A similarly slack wind gradient will lay down over the whole Iberian Peninsula during the swell.
At Nazare, which will also peak in size on Thursday, this will play out with the wind turning light north-east late on Wednesday and then swinging between light south and south-east - which is straight offshore - through Thursday morning before a late seabreeze. Most large Nazare swells are accompanied by wind from the northern quadrant, with quality determined by how light it is. It’s very rare to have a swell of this size accompanied by wind from the southern quadrant.
So...size? Nazare is one of the trickier waves to accurately forecast owing to the process of constructive interference that makes its peaks stand tall. The Alpine wave size is reached, not simply by wind strength, but by two lines of energy - one incoming, one refracted by the Nazare Canyon - interfering with each other. It’s a wedge by any other name.
Coastline to the immediate north and south of Nazare should reach 30ft on Thursday, meaning the peak at Nazare should be in excess of 50-60ft. Wave size will vary with the angle of incidence.
The swell will also brush Europe’s western islands with a short-lived swell in the 15- 20ft range hitting on Thursday.
Further south, across the Strait of Gibraltar, won’t see as much energy as further north. The storm won't quite form far enough offshore for significant spread, but nevertheless late Thursday to Friday morning will see parts of the Morroccan coast between 10-15ft though the swell will be short-lived.
Swellnet wave model - Bundoran, Ireland
Swellnet wave model - Hossegor, France
Swellnet wave model - Nazare. Portugal
Swellnet wave model - Oualidia, Moroccco