A large black blob is heading across the North Atlantic, generating huge, bumpy surf for the north west of Europe and a big, clean swell for the south.
There is a deep low positioned about 900km south of Iceland, with a strong westerly fetch on its southern flank. The system has already generated a large swell, enhanced by the dynamic fetch as the low moved from west to east over the last couple of days.
The system has now turned northwards and is expected over Iceland by midday tomorrow. The fetch on its southern flank is still active and pumping out swell. High pressure is also building from the south, creating weak pressure gradients south of the English Channel, and allowing the swell to propagate towards southern areas relatively unhindered.
In northern areas, expect a huge, long-period swell arriving overnight tonight, with wave heights at westerly exposures exceeding 30ft. The swell continues through tomorrow, accompanied by gale-force west-southwest winds. Wave heights decrease steadily on Friday but wind conditions improve, with strong to gale-force southwest or southerlies.
In the south, the swell hits from midday tomorrow onwards, and keeps pumping all day Friday. Expect a large, lined-up swell with periods up to 20 secs at first, steadily decreasing. Winds are not so much of an issue as in the north, with light southerlies in most places on Friday, swinging southwest in Portugal.
The overall best bet will probably be around the Basque Country, with big, clean surf, exceeding 15ft at many spots on Friday.