North Atlantic storm

46°47.4′N 008°18.5′W

Waves left about 20 Sep 02:18Z, ± 3 h

Placed by 6 buoys, whose own placements lie within 720 km of it

Each buoy places the storm from how its swell's period shortened as it arrived: the longest waves travel fastest. Fronts are drawn at deep-water group speeds along great circles, and stop at land. How it is worked out