North Atlantic storm

11°39.4′N 017°42.3′W

Waves left about 18 Sep 03:37Z, ± 7 h

Placed by 2 buoys, whose own placements lie within 455 nmi 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